HD-6B /AG Engine swap options

https://www.ebay.com/itm/TRW-T7997H-STD-TWO-Piston-Rings-Set-For-Various-Allis-Chalmers-2Cyl-Engs/402515754368

I'm planning a "poor man's rebuild" on an 11000 engine, in-frame:

Mine is an HD-6B that already had an engine swap to a HD-6AG engine.  I believe it has a dry clutch.  I am thinking maybe a 3/71 detroit.  They are about 300ft/lbs of torque at 1400 rpm which would probably be all I need.  My understanding is a variation of the 7000 engine was used in Army generators in the 70s and maybe into the 80s.  It looks just like the engine in mine. 

I agree with Coke on the 4-71 option providing there is sufficient room, I'm not too familiar with the dimensions under the hood. Don't forget, however, if you go with a 3-71 you can comfortably run 70's injectors giving you more HP. You would be easily over 100 HP if you do. Using an ideal timing pin will wake it up too. I have played around with injector size and timing on 6V53, 6-71 and 8V92's and the Detroits are great to work with... as the old saying goes about them "you either love'm or hate'm" LOL. 

Several places seem to have 2 stroke detroit parts.  AC parts.. not so much.  I just wonder if a 4//71 will fit. 

Always wished the townships old AD40 I plowed snow with in the late 70's had a 6-71...maybe even a "T". Hit the drift with the V plow in 6th and drag down and slip in 4th for a little more then back up 1/8 mile and get another run at it!

I have a friend with a 4/71 that needs rebuilt.  Not sure what era but he has an AC bellhousing with it and most of everything it needs to run.  I missing an exhaust manifold and maybe a couple other small things.  I am away from home.  I can't find dimensions on the 6000 or 7000 engine (length/width/height etc) Can someone throw a tape measure on theirs and post the dimensions (rough is good enough)  4/71 dimensions are not hard to find, I found those.  Next question - a 4/71 makes around the same torque as the turbo engine I have so I suspect I probably won't break things if I take it easy.  It already just spins the tracks without really trying.  A 3/71 probably would be ideal.  Torque is a bit less then my engine but has good horsepower and we know it will fit if I have the right pieces to connect everything up. 

What about a 4BTA Cummins?  Key will be finding a correct bellhousing for the SAE 2 clutch setup.  What about a Deere engine?  I haven't had a chance to work on it but I am going to do some measuring while I am home and move it somewhere where it will be possible to work on it.  Still runs great but with water getting into the oil I am just moving it carefully around so I don't do further damage.  It could be just a head gasket.  It wasn't doing this until I changed the oil. 

On the original HD6B where is the hydraulic pump mounted? One benefit with Detroit engines is having several options for accessory drives, some other makes don't seem to have more than the front pulley to drive the pump.

The greater reason I ran this thought on the 336 Case is that there should still be quite a few around compared to the A-C engines. I've had three 680 Case backhoes (still have one) with this engine plus one stationary set up. One I had to rebuild but the rebuild kit was reasonable. The root cause for that failure was neglect in previous ownership, cracked liner with A/F in the pan. Some have had this 336 fail due to diesel fuel dilution into the pan. Older used units that slightly increase the oil on the dipstick while using a bit of oil at the same time eventually end up with enough diesel in the bottom that the bearings fail. This can happen to any diesel and the problem is easy to address if caught in good time. Overall the 336's have been good performers for me. The engines in the backhoes have the smaller bearing journals but farm tractors, I believe, as well as for sure bulldozers and loaders have the bigger journals for heavier work loads. 

Tractor # 18906 would be a 1965...   Per Swinford's book.