As a proud owner myself, keeping it stock has its merits until you get absolutely dusted by a 4 door V6 Civic. The way I look at it, Olds built 4208 great looking, riding, '87 442s. I've got all the numbers matching stuff mothballed for posterity [for anyone that cares] and will soon have an even better looking, handling, and braking '87 442 that will now run like a 442 should.
Heavily beefed small block or a mild big block either one is my vote! And you can indeed keep it Olds powered. 😎
But, it's all good. Glad you found her . . .