As fas as I know, the frames were all the same in the front engine area from 1984 to 1993, or first generation S10/S15, vs. Luv. The frames from behind the front doors would vary between the various cab and box designs. I don't know about the Luv frame. Engine wise, the oil pan would be my concern, as I don't know if the oil pan in the Luv is the same as the S10.
So the frames were the same in the S10/S15, whether it had a 4 or 6 cyl. Mine had a 6 in it, and underneath the motor mounts were holes for the 4 cyl mounts, which also fit the diesel mounts. The motors were adapted to fit the truck, basically.

The engine should phyically fit in there no problem. The engine won't go in or out with the transmission connected. You will have to do custom things, like adapting the wiring harness to work - easy, cause you-re using less of them compared to the gasser - and other minor details. Typical swap thing.
Oh, I think I had to move the cross-member under the transmission back to the next set of holes, from the auto to the manaul.

Does this help? <img src="/forums/images/graemlins/kewl.gif" alt="" />