How about a 4bt Cummins? I didn't see it mentioned but it's lighter than the 6bt (just as durable too) and should be tunable to around 200hp.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k