Build 37A or 39 B?

Thanks jd b puller for your input. I have a 1939 JB B and A 1937 JD A.
What to build one of them into a puller.
The class choices are 3500 4500 5500lbs.
For the 37A I have a heisler head for it, also have a 44 a for parts ( if any can be used)
For the 39 B I have a 5-2 power block was told that it will bolt in. And drill bottom holes
Any have late b for parts( if any can be used)

So I what to build some power,
don"t what to build the biggest tractor out there,
What to stroke it,one that will not require me to move the camshaft.What it to last, will be running stock rpms.

Who is a good person to have my crankshaft work done by, what kind and lenght of rods, pistons?
The 5-2 powerblock is in a tractor at this time that runs.
Welcome any and all commits ideas and suggestions