ok if you want a V8 for your Hbody your going to have to look Cbody which is practically the same thing.
1986-1993 Cadillac DeVille is what you are going to have to look for.
1986-87 had the 4.1L
1988-90 had the 4.5L
1991-93 had the 4.9L
you can use any of those engines just the 4.1 are notorous for blowing up unexpectedly. The 4.5 got better but still had issues. So i would recommend the 4.9.
The engine and trans will bolt right into your car. NO custom mounts should be needed. i would recommend getting a donor car so that you can have all the wiring and note the differences. You may have to swap over the front suspension and brakes but once again it should just bolt on.I have not tryed this swap yet but have been thinking about it and looking into it for a while.
Here are some of the problems with the 4.1 just in case you decide to use one (please dont)
1) The sand-cast aluminum block was so porous engine oil would sometimes seep right through it. This was "to be expected," according to the Cadillac Service Manual (citation needed).
2) If the engine were not stone cold when the heads were removed, they would never again align properly with the block.
3) The camshaft was mounted on babbit bearings. Removing it destroyed the bearings. A warning not to remove the camshaft was eventually cast into the block.
4) Because of the high operating temperature, sludge built up quickly if the oil were not changed frequently. At the same time, the holes that drained oil from the rocker panels to the crankcase inexplicably intersected two of the head bolts; the oil was expected to wend its way along their threads until it eventually found its way back to the sump. Thus the slightest amount of dirt or sludge was sufficient to plug these holes and cause oil to pool in the rocker panels, starving the crankshaft and main bearings of oil.
A mechanic familiar with this engine would have to make sure the engine was stone cold, and then a)remove the two relevant head bolts, b) ream the holes with a bottle brush, and remember to c)avoid torquing these bolts to the 95 ft-lbs specified in the service manual unless he wished to Helicoil the stripped aluminum threads deep in the block.
5) Clearance between the piston and combustion chamber was so minimal that carbon on the piston would make the engine pre-ignite badly (other GM engines also had this problem). (citation needed). Thus the vehicle had to use premium gasoline at all times. The carbon could only be removed by either a) removing the heads, or b) pouring GM Top End Cleaner, a potent solvent, into the throttle body with the engine running. If all went well, the engine would produce huge clouds of white smoke and run better for a while. If all did not go well, it would go into hydrolock and seize, never to run again