The chevrolet based Mercruiser engine is a relatively high performance engine (140 hp). It is made to run for long periords of time at 4,000 rpm. It should be available on the used boat engine market. i
I think the bellhousing bolt pattern is different from the Fiero transmissions. Also, the cam grind is designed to run at high rpm while under constant load. A boat outdrive is under a constant load in order to keep the boat planed out. You don't have that load when cruising in a vehicle so it would be very similar to just revving the engine to 4500 rpm and holding it for long durations. The engine wouldn't last very long. Changing out the cam may be an option.
Automotive and marine engines can be interchanged with slight mods. I found that the 4.3 V6 truck engine specs were identical to my 4.3 Yamaha engine. Everything in the engine was the same except for the camshaft. Same crank, rods, pistons, oil pump and heads. So, I would assume that the engine could be reverse engineered to go into a car.
The major thing I found that was different in the truck and marine long block was the price. $850 for a reman truck short block as opposed to nearly $3000 for a reman marine long block.