I am rebuilding the two engines I have ---one chassis.... and I have already bead blasted, primed and painted all the pieces. My question is to the use of stainless steel nuts and bolts for things like the water jackets, oil pan, etc. Will these be the correct "grade"?? or should I use regular zinc coated grade 5 or grade 8 fasteners???

Of course these will not be "Correct". But I use them on everything because they will not corrode. Better than was used back then. Have rebuilt two engines using SS on pan & water jackets. No problems. Think they are stronger than original so be sure not to strip threads in alum. Good luck. And SS bolts are more purty.