Yeah, 91 was a bastard year. LA block, but with a magnum style serpentine belt setup. Like everyone has said, I'd go with a magnum motor. You can drop that 94 in there, and just go with an aftermarket intake, Holly Carb and HEI distributor. That's what I did on my 90 vert, albeit I kept the older LA style V-belts as I had a crate motor already set up that way. But with the Serpentine, you can even keep the stock clutch fan and it'll all fit nicely in the 91.