John Deere 420 Engine

[JWKrische]

I'm new to this group and have a '58-'59 John Deere 420. The gear on the bottom of the distributor broke, which caused the oil pump to stop and it locked up the engine. Where's a good place to find used blocks? Are there any complete repower engines for this model? I would rebuild this one, but when my Great Grandpa got it in the '60's he repaired a crack in the water jacket in a very unconventional way. Needless to say, although it worked for the past 80 years. I don't want to sink a lot of time and money only to have it start leaving again.