Circle D specializes in converters for E4ODs and 4R100s for GEN 1 and GEN 2 Lightnings. They have a higher stall speed (your choice), billet front cover, fully brazed internals and 3 or 4 clutch configurations that is far superior to the stock, single disk converter.
It's likely that the block in that truck is an F4TE casting and will accept a roller cam conversion relatively cheap. I have purchased several used sets of roller accessories for less than 100 bucks; roller lifters, spider and dogbones. You can find these parts in mid 90's F-series 5.0 trucks and 87 and later 5.0 mustangs; just keep an eye out on ebay, craigslist and/or the corral. You'll also need to change the distributor gear out to a steel piece if you do go with a roller cam.