I have a 1988 Chevy S-10 with 4.8 engine and auto trans. Is it
possible to convert this to a 5 speed with clutch without to much
trouble?

Define "trouble". It would be a LOT of work, both mechanical and electrical. Probably be easier, faster and cheaper to go buy a vehicle with a manual trans. If you decide to go ahead with it, make sure you tell the parts people you have a 4.3L engine, (not 4.8) ;)