I was definitely surprised that it was a 3.1, I was also expecting a 2.8 but it is in fact a 3.1, on the multiport fi 3.1 what do I need to do about the intake manifold to have the throttle body towards the front?
Isuzu P'ups definitely had a GM 3.1L V6 option. If you want multiport, you're going to need to find a Camaro/Firebird. The FWD engines have aluminum heads and the intake won't bolt to the RWD heads. FWD blocks do not have provisions for the RWD motor mounts, so swapping the whole motor would require some fab work.
There are options to use FWD parts. Years ago I built the Franken60, that used a gen1 block, gen2 internals and a gen3 top end. I also added a small turbo for good measure. The combination was never optimized, but made about 250 HP and 300 ft/lbs. If I used better match injectors and actually tuned it, I bet I could have gotten around 300 HP with the limit being the turbo mostly and then the small port gen3 top end that I used, large port would open up much more potential.
IIRC the Isuzu uses a FWD style block, with the starter on the left side, but I'm not sure about the block where the mounts bolt up. If I am correct it might be fairly easy to swap in a gen2 60 degree V6, gen3 would be more work, since the block is different again where the mounts would be concerned.