+1Here is my problem with engine swaps; If you need a car now, don't swap an engine into something. If you don't need it now, My choice would be a slight downgrade to a 4.3, those are pretty good on gas (I have a 4.3 Blazer, it get's 18-19 occasionally). But even a downgrade is gonna take longer than a snap of a finger. It's just not justified to me, all this time and effort for 3 MPG.
In these threads about swapping motors for better MPG, I always ask if the cost of the swap is worth the savings? What is the ROI or return on investment? Granted as the cost of fuel rises it makes it more attractive, but its really just an expensive experiment to see if you'll get better gas mileage.
The caveat always being what you have available to you.. maybe you already have the donor veh with harness and ecm/pcm's, all the tools needed to fabricate the adapters and mounts you'll need.. and exhaust
If you have to buy all that stuff, the costs add up quickly.