Will a 1998 5 spd std 2wd transmission 4.3 l fit in my 1988 4wd std 5.7 l

if its the same one minus tall housing..

It won't work unless you want to make your truck 2wd. Otherwise you would have to change the tails haft and output shaft. Which is about as easy as fixing the original trans

My web searching tells me the bell housing is a bit thinner, np and the tail shaft is longer on the 2wd. Can I cut the tail shaft and still have enough spline length to work with? They say you need to cut 1.5 inches leaving 3 inches to work with. Thanks

Never heard of cutting it, doesn't sound like a good idea

you mean the driver shaft IMPUT YOKE ??