If i had a just about stock v-8 vehicle and I wanted an inexpensive performance mod, I would put nice big gears in the rear. Nothing else you can do for that small an amount of money will produce such noticeable results.
Just my opinion here...my experience has been that often times 30 year old, heck even 20 year old engines have lost some power over the years, particularly noticeable in the low rpm performance. But, the mid to upper range still performs pretty good. And by putting bigger gears in the rear, you get to those higher rpm's much faster. Of course I wouldn't want to frequently explore the more strataspheric rpm's in an engine that old....
A good shift kit would be another inexpensive yet noticeable thing to do right around the same time.