The early Sevilles were based on a modified Nova chassis. I would suggest some research that is off of the keyboard...real lift the hood and look type stuff. Since you have the Seville, finding a similar Nova to look at should be a snap. IF the front crossmember is similar, it may be as simple as bolting in the Chev motor mount plates. The other consideration is the distance from the transmission flange to the motor mounts between the two engines.....again, a sneaker search. This should get you darned close. It may not be a bolt in but I'll bet that it is a weld in with minor welding.