I'd probably go with the power pack heads, a cam with some bottom end torque, a used Performer RPM intake...they're the most common intake around--you should be able to find one in the local bargain shopper, craig's list or ebay for less than $100...easily for less than $100.
A set of shorty headers will also help, or, if you've got some extra money, a set of 2.5-inch rams' horn exhaust manifolds. These are the bigger ones, and are more expensive. Ebay prices are goofy for them, but new ones from YearOne are available, though they're about the same price (nice and clean, with no breaks or rust pits though).
A small 4bbl carb and HEI ignition system would also be the right choice.
Go with a new, 4-row radiator, make sure it has a fan shroud, and spend the money for a fan clutch and an OE-style 7-blade fan. The fan and clutch will be more expensive than you want to spend, but you'll really enjoy it in any kind of traffic or driving up mountains on a hot day. Also, I tried getting a fan from the junk yard, and really paid attention to get a straight one--both were bent when I saw them spinning on the engine. Buy one from a resto supplier. Again, I got mine from YearOne (I work there, but I'd have gotten it there if I didn't, because I was able to research exactly what I needed in their catalogs)
Sounds like a great truck!
-Brad
Oh, and I agree with whoever it was that said upgrade your brakes.
