MARLIN - Guy from around Prophetstown, IL, Bill Newlon used to pull a Minny UB with an Allison 1710 CID engine in the 1960's, and in the early 1970's bought our next-door neighbor's G1000 and dropped an Allison in it. Some guys used the Rolls-Royce/Packard 2490 CID V12 from the later version P-51 Mustangs, MORE HP... One guy I mentioned with the twin Allison tractor had a matched pair of Allison V12's from a P-38 twin engine fighter plane, one rotated clock-wise, the other counter-clock-wise.
The announcer at the Henry County, IL. fair pull most years was an old local boy, forget his name, but I guess he almost married my aunt, and he was in the Air Force during WW II and knew all about those engines. Post WWII when jets became common, new-in-crate surplus Allisons would sell for $50 each, the main & rod bearings were very high in silver content, and many of those Allisons were "disassembled" with sledge hammers just to get to the bearing inserts for their silver.
Here's a link to a thread on YT about Bill's Allison powered Minny's. The thread also mentions Bill & Perry Noord. Bill & Perry's wives were nurses at the hospital in Geneseo and my Mom worked with then, good friends actually... we always rooted for Bill & Perry, and since they traveled with Bill, rooted for him too. Last time I saw Bill pull his G1000, I think the announcer said he was 78 yrs old. The Allison needed a good tune-up, but actually ran better than it did most nights back in the 60's & 70's.
http://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=mm&th=66448
One of the neater pulling tractors was a Farmall M, think it was painted white like a 1950 Demonstator for at least a couple years, WFE of course, and in place of the little 4-cyl. 248 CID IH 4-cyl, they dropped in a V8 Ford GAA V8 displacing only 1100 CID, 1000#/ft of torque, and 450-525 HP @ 2600 RPM depending on the tune.
http://en.wikipedia.org/wiki/Ford_GAA_engine
He pretty well had ALL the competition covered on HP & torque except the twin engine tractors like Bill & Perry Noord's W9 IH & Massey Harris 55, Massey had a pair of 427 Chevy's, W9 had a pair of 409's, And the airplane engined tractors like Bill's Minny. I bet that M rearend was screeming UNCLE with ALL that HP & torque going thru it!
I'm glad people are hunting up those old pulling tractors and restoring them now days. Took a LOT of time, money, and engineering talent to get those tractors to run reliably a couple nights a week all summer long, plus the time and money to haul them to pulls all over the midwest. It's nice that people now days remember those pioneers of tractor pulling.
To keep this post somewhat on-topic, there were always 3-4, sometimes more 4020's with 318 Detroit diesel conversions pulling, some of Jon Kinzbaugh's handy work. Neighbors who farmed the 320 acres across the road pulled a pair of turbo'd 4020's. Rather crude, used a turbo off some BIG Cummins engine, had to cut a hole in the hood to make it fit, ran a bunch of 4" dia. tubing from the HUGE dry-type air filter bolted to the tractor's frame to feed the turbo. My cousin was good friends with them. They "Farmed" with them, engine tuned for roughly 250 HP, pulling they tuned for 450+/- HP. Those two 4020's were probably the only farm tractors in the county that needed more mechanical work on them to keep them running than Dad's 4010.