I was looking at a website that has cadillac engines (rebuilt) for sale, and they list a 4.5 liter engine as an upgrade to 82-84 RWD cars originally equipped with the ht4100 engine. Anybody had experience with anything like that? I would think the increased displacement would put the stock computer into panic mode.
I don't have any first-hand knowledge of the conversion or the platform, so this is just guessing. I suspect the hard part would be getting the physical parts like motor mounts to line up, but they may have simply taken a 4.1 block and bored it to 4.5 specs, or they may have drilled new mounts in a 4.5 block. As for the top end parts and engine management, TBI is pretty simple technology, and my own experience is that you would just need to use the old sensors and some 4.5 TBI injectors in the throttle body, and it will probably work. There might be some small problems with bosses and studs (the alternator mounting bracket changed, etc), but that part of it should be doable.