You know already that it's loud. Otherwise it's fine. There are an awful lot of very expensive race engines that run unbaffled; there is no risk to the engine. The "backpressure" argument stems from a misunderstanding of the relationship between exhaust restriction and scavenging. Scavenging is good, backpressure itself is never good unless it happens to come with enough scavenging to offset the ill effects of the restriction. I'm not sure why everyone wants to believe this backpressure business; I guess we are attracted to the counter intuitive like "Could water boils faster than hot water". It sounds so strange it just might be true. With a good set of longtubes you are getting about as much scavenging as you ever will, so before anyone suggests you'll make more power with an exhaust on there, I'll say you're fine... except for having to live with an obnoxiously loud truck.
I ran a 78 with open longtubes for a couple years and the problem is that it's just deafening, at WOT it could be heard for miles. Not even remotely legal for street use. Also if you aren't getting exhaust out from under the car it tends to make its way inside.I'm probably one of those guys that doesn't fully understand the difference, but have read pros and cons to both sides. However, I've heard/read enough horror stories to not be willing to take the chance with something so easy to 'theoretically' prevent. Not to mention, I figure if there were absolutely zero negative effects, there would be a lot more folks running open headers and Ford would have made open headers an option.
Backpressure does not make power. This has been debunked many times over.You loose a lil HP tho since u don't have any back pressure. I'd recomend atleast putting some kind of muffler on it for the back pressure.