I "need" to see a picture of this truck. Assuming that you put a small block Chevy V-8 in it, I'll guess that you may be good to pull an 8,000# trailer with no issues. The frames on the trucks back then aren't as strong as they are today, so you need to be a little concerned about that. An 8,000# trailer would have 800# to 1,000# of tongue weight. As long as your truck will handle that weight, it should be fine. It sounds like you put modern axles under it, so it may do just fine, depending of course on what you actually did to it. A trailer properly set up with electric brakes should help the towing situation.