which engine will fit
You didn't say what kind of car the 88 5.0 came out of...if it's from a Mustang, Thunderbird, or Cougar XR7, it's an H.O., (351W firing order, forged pistons, roller cam and lifters), definitely an improvement! Check out your heads, they should be the same, (E5TE or more likely E7TE). It's going in a truck so, because you have the space available and because it has larger runners, I would upgrade to a 70mm throttle body and use your existing intake...I would also, however, look into camshaft options. There is a big difference in weight and gear ratios between a Fox body and an F-150!!!