PB blaster will be useless as it wont reach the threads of the bolt. Do yourself a huge favor, and buy a MAPP or propane torch. I literally just did this on my bronco last week. I had no problem with all of the bolts, but one!!! I let PB blaster sit on it for two days, still didn't come loose. I hit the block with the torch for 30 seconds, and she popped right out. You need to be careful. If you come across a bolt that won't come out, you better stop and have some patience otherwise you'll be stuck with a broken bolt, and no one wants that. If you're going to get in there and take everything apart you might as well replace everything you're going to touch. Radiator hoses, water pump, by pass hoses. Hell you should replace the thermostat while you're in there. If you're going to be taking the timing cover off, then I suggest replacing the timing gear and chain as well, as someone mentioned. It's very easy. You will need a puller to take the harmonic balancer off, and you'll need lots of RTV to seal the timing cover to the oil pan. You will also want to replace your front main seal since you're going to be there anyways. Word of advice with the RTV. Let it set up for 5-10 minutes then start bolting stuff down, and as soon as you see RTV to ooze out stop and let it setup for 45minutes to an hour, and then torque everything down to specs. This will ensure a leak free install. People who bolt everything together while the RTV is still goopy wet just push the RTV out of the way, and there is not a proper seal.
If you break a bolt, do not panic. Panicking will be your first idea, but do not panic. Grab a beer and take all the other bolts off that you can, and if others are stuck, use the torch. If you break another one, you can probably panic a little bit, but it doesn't help. Grab another beer. Do you're best not to break the bolts. But if you do, remove the timing cover with a prybar, or rubber mallet, or worse case scenario beat it to death until it breaks off(then replace with a new timing cover.) Then take your torch and heat up the block around the bolt, and hit the bolt with a paraffin wax candle. The bolt should suck up the wax, and the bolt should come off super easy using a pair of vice grips as close to the block as you can, while turning slowly. If that doesn't work let it sit with PB blaster for a few days. If that doesn't work you can make you're own concoction using 50% ATF and 50% acetone. This will usually work better than PB blaster or anything for that matter. But using a torch would be the best option. The idea is to heat the block up around the bolt rapidly, so that the rust bond between the bolt and block is broken, allowing you to turn the bolt. You do not want to apply direct heat to the bolt itself. I always leave the flame in one spot. If this still doesn't work you can use a can of compressed nitrogen (keyboard cleaning spray held upside down) to freeze the bolt, and then immediately heat the block to increase the effect.
If you go through all these combinations and still haven't gotten the bolt out. Stop drinking beer, because the next part will need steady concentration. Cut the bolt as flat as you possibly can, close to the block and use a center punch and punch a hole as close to center of the bolt as you possibly can. If you haven't guessed you will have to drill the bolt out. This isn't as hard you might think. If you could find some reveres drill bits, that would work even better because the action of drilling might actually loosen the bolt. I used a set of craftsman drill bits that are extremely hard(i forget the material off the top of my head) and cut through anything. But the harder the drill bit, the more chances of breaking it in the bolt. That is bad!! You need to drill a smaller hole first, probably 1/16th of an inch. This is the hardest part, as these smaller drill bits are more susceptible to breaking. Use a cutting compound if you can. Hold the drill steady with mild pressure, and keep the drill speed in a medium speed. You want to keep the drill as straight as you possibly can. I will repeat that, drill as straight as you can. Once you drill in as far as the depth of the bolt, or as you feel comfortable, bump the drill bit size up one size, and drill it out again. Keep doing this until you are one size smaller than the bolt you broke. At this point, you should be able to fit a tap in the hole, and chase the threads, and then you are done. If for some reason you drilled off center, or not straight, then you will have to drill the hole out, and tap it for a larger bolt. You will also have to drill out all the other pieces as well; the timing cover and water pump to accommodate the larger bolt. Put everything back together with WD-40 or PB blaster on the threads to reduce the risk of future rust.
If you break a drill bit in the bolt, you are fawked and will have to try your best to get it out with various carbide dremel bits, and drill bits. Good luck with that. If you are not an idiot (i am not calling you one, just being general) and you take your time you should be able to accomplish this with relatively low stress level. As always, when you are done with the hard parts, drink a beer and finish up the project. I would suggest reverse flushing your heater core and block. Put a hose on the return line from the heater core (the hose that goes from the heater core to the water pump) and pump some water through until the water coming out is clear. I would do the same for the radiator as well.
Make sure you torque everything down properly, you wouldn't want to take everything apart again would you?
Good luck, and have some confidence, it happens to all of us.
