Identification on farmall 100

The correct block part numbers are; for a 100 is 354898 R2 or R3, 130 is 366204 R1 and 140 is 367825 R1, R2 or R3.

People are offering to sell me all kinds of casting number blocks. Prices are all over the board.

What are the pitfalls & benefits of changing to another casting number block ?

Mine is an "R3" that had a dipstick hole plugged with a cork plug, yet it had the "two faucet" oil pan.

Center main journal had spun the bearing over the years. Rebuilder says he can put a spacer block in the bad journal, re-line bore it, and put it back togethr correctly -- however adds that this would add maybe $700 in machining costs.

any adivse ?

You can use the 130 or 140 block, however you'll have to match pistons and sleeves for those blocks. There is another snag with a 140 block, 140 used an automotive type water pump on the fan shaft. I don't think you can change that to your pump, hole in block not drilled right for your system. I'm also not certain a 140 fan will match up with your rad and shroud. I have both 130 and 140 but I've never had them apart at same time. Near as I can tell that one may cause you grief.