Did the same with my 91 Roadmaster. Did the conversion cheap just to see if it worked and ended up putting on over 100 K on the clock. If it was powerful enough to tow my new trailer (never could find enough room under the hood for a turbo) it would still be on the road. Makes a great conversion and expect in the mid 30s for fuel mileage.
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Bill
91 Buick Roadmaster/Avant 6.2 NA conversion (gone but not forgotten)
94 Cadillac Fleetwood (sold)
08 Aerolight 23TT
06 Vortec Max Silverado CC SB (sold)
10 Avalanche (electronic quagmire but love the truck)