I had an 82 Buick Riveria with the diesel that wouldn't get out of its own way. I bought it with blown head gaskets and found out the heads were cracked. Found out almost all of them were cracked but didn't cause any problems. I replaced the head gaskets and the car started every time but had no power. The 260, 350 and 403 blocks were all the same as the diesel, just different bores and cranks. I replaced the diesel with a 403 from a trans am. The 403 fit perfect with no modifications except rerouting 1 wire from the injection pump to the distributor. Fuel lines fit, exhaust fit, stock 403 motor mounts fit. Cleaned Fuel system and was riding. The only problem I had with the care after the conversion was breaking front axles because of the torque of the 403.
Later I had a 83(?) Cutlass V6 diesel which served me well. It was basically the same engine with 2 less cylinders but had been refined and gave great service. It even had plenty of power. Both engines had the same injection pump design which needed rebuilds about every 100K.
I personally would run from one with the 350 diesel or just plan on replacing it as soon as you get it.

Paul

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84 500 SEL (307,xxx miles)