Don't even consider a 2.8L.... 4.3L would be the better way to go. Easiest swap would be to get an engine/tranny combo that way there'd be no worries about compatability...... Or maybe just go bonkers and slip a late model 5.0L (305 cu/in) V8 in the engine bay....lotta info on the swap. The 4.3 is simply 3/4 of a 350 so why not add the missing two cylinders as part of the swap?
Have you looked up any of the GM 2.5L/Iron Duke/Tech 4 info on the web? This engine will never be a hotrod but you can work some magic with it...... believe it or not you can buy some performance parts for this engine...... just a thought.
mike