1939 John Deere B question. engine rebuild help needed

Ok guys,, long story short, me and my dad bought a restored(repainted) 1939 john deere B from a family friend,, tractor ran perfect ,, well after a couple weeks I went out to start the tractor and some shuttered when tractor first started then tractore shut off,, to skip ahead I pulled the crankcase vent cover off and low and behold the left piston and rod are laying in the bottom of crankcase,, they are both ruined,, the left cylinder skirt is ruined, it appears that over time or some time in the last 50 years somebody either didn't put any cotter pins in the nuts of the connecting rod or they fell out, there was no cotter pins in either connecting rod of the two and we think a nut backed off the rod bolt and finally turned loose,,we found one bolt laying in the crankcase untouched, it could have ran for years with only one rod bolt as far as we know.. ,,, so here is my question, the right side piston, rod etcetc is fine,, my question is whats the best way to go about this as far as rebuilding,, I have been looking a 1305r block(used for $300) ,, I have found a used b5r rod($75 with wrist pin and shims) that is suppose to be the right rod for the engine and I have not located a piston b1308R,, am I gathering right stuff in the right way,, and the crank journal on the left side has one scuff on it, it is visible but you can BARELY feel it,, I have let several mechanic buddies look at it, half say it could be a problem other half say throw a rod on it and run it, because babbits are not that precise to start with and tractor only turns 900 rpm,, this is just a crank every couple of weeks tractor,, Im just sort of overwhelmed with the hole ordeal.. any guidance or advice would be appreciatted.

Maybe if you can find them a used rod,piston and have the block sleeved. Make sure they sleeve all the way to the bottom as the oil ring goes clear down and almost out.

Clean up the rod journal with emery ( suspose to use crocus ) cloth and mic it.

Jon. Where are you located ? I'm in Western Nebraska. I known where there's two 41 Bs are at. Not sure if parts are the same or not I can check. There's also another B not sure on year but its electric start. Maybe late 40s or early 50s ? Email here doesn't work but you can email me at [email protected] if you'd like include a phone number. I may be able to help you out.

I live in North Carolina,,,, I have found a set of .45over pistons ,, for a 39-40 b,, they say the way I understand it the 39 model was a odd model and used most of its own parts,, I was thinking of getting the used block and having it bored out to .45 over, and use that piston set,,,,,, but i didnt know you could sleeve these blocks??????? I wonder what thta would cost if I had it sleeved.

Your 39B is basically the same as a unstyled B.

Is the engine stuff also diffrent??? pistons, rods. etc.etc