I went back and forth at least 50 times finally went the 4bt route if I had it to do over again honestly I think I'd gone 12v but it's still a toss up. Obviously I would not have had any concerns w/ axles etc. the way it ended up. I would have probably been forced to swap to a ZF5 out the gate but I would have sourced it with I got the engine so that wouldn't have been an issue.
13 inches of vacuum at idle is really low. Those durations you mentioned didnt seem all THAT big... I'm running I/E durations of 222 @.050 in my 300, 280 gross duration. 110 LSA with a moderate .480 lift. I pull 17" of vacuum at idle. I doubt your brakes will like only 13", unless you're going hydroboost.
The cam was spec'd for good torque all the way up the curve and hp all in at around 5k. A different cam and it would have been over 700hp easily. Built to be a great daily driver running on reg octane gas. As for the vacuum, I am going to start with a can and see what I got for brakes. The vacuumn advance was disconnected just for the dyno testing it will be hooked up for driving conditions.
I think your brakes should be fine with that much vacuum.
Mine only has around 6" and the brakes work ok the only time i notice a stiff pedal is in town at a light, moving up because a vehicle moved up, the pedal is good on the initial stop but can be stiff on the move up after they move.