I have a L67 (SC 3800) in my '86 SE. Its not the most straight foward swap but it is do able. Including the price of the motor, expect to pay around $3k. One thing I would be worried about is how long that trans will hold up behind the new found torque. The isuzu is notoriously the weakest trans. If you baby it literally all the time, it could hold up, but wheres the fun in that?
If you're serious about doing it, contact Loyde at fast fieros (
www.fastfieros.com) He can help you with all your wiring/ecm needs for the swap and is a great guy to deal with.