A well maintained 360 will always treat you right. The lower horsepower torque numbers that you see attached to most of the later model motors has to do with how they are rated as compared to "the Old days". Also they are bogged down with all the smog junk.
If you can de-smog it where you live and get away with it, you'll notice significant improvements in power.
A good intake manifold and a decent carb will also be a big improvement. For even a mildly built 360 I don't think dual pipes are needed. A good flowing single 2 1/2"-3" exhaust gives good flow, enough back pressure and plenty of torque. Some guys are also running throttle bodies instead of a carb and have good results.
A little sprucing up of the ignition system will give you a little better mpg's and a lot better response. There's a lot of options out there on that.
I am running headers as well & for my truck I think that was a waste of money. They sound good, but the AMC exhaust manifolds flow well as is and give a lot less headaches as far as exhaust leaks go.
The TF727 transmissions are solid, but suck for what I want. The ratios aren't deep enough for me. I am doing a NP435 manual transmission swap here soon for better wheelings gears and no torque converter power losses.
Something to think about when buying your truck is the axle ratios as well. The "tow-package" wags will have 3.31's and a traclok limited slip in the rear(most likely) where the non tow-package will have 2.72 and an open rear end...but don't quote me on that. An easy way to tell is there will be a warning sticker in the back of the glove box that says something along the lines of "vehicle is equipped with a locking rear differential". The 3.31 equipped wagons seem to scoot on down the road a little quicker and are better for towing. There is a tag on the diffs that say what the ratios in them are but most of the time they are long gone. If you want to go to bigger tires, gearing is something you should take into account.
There are some great points in the previous posts and the things I put down are things that came to my mind.