Also be aware that really only the block and cylinder heads are the same. Manifolds, oil pans and some accessories will be different on the tractor vs. the harvester. If you already have the gas tractor you can simply just swap the parts around from one engine to the other.
We kept one of those old 105 engines around for years thinking someone would need it. After a bunch of years passed with no takers we finally sent it to the scrap yeard.