will a 350 block off a 98 gmc 1500 fit on my 89 corvette

Sometimes there are differences in the block castings that are vehicle specific so be sure and compare the two side by side. You might be able to work around some of them but some might be difficult to deal with.

WHY???? If your engine needs replacing, either rebuild it, get a crate engine that can drop right in and run, or get a rebuilt engine for your 89 Vette. Putting a truck engine into a Corvette is not only a sin, but like the wise people above said, will be problems by having to change everything out to make it work. Chevrolet and GMC make similar engines, but there usually some subtle differences and parts may not fit/work properly. Save yourself a lot of headache, and stay with what is make for your car. Less expensive in the log run. CorvMC, no!