Bought a likecnew SRS 621 fom a ffiend. Each time I try to download an operator manual it refers me to the SC 621. What is the difference? I undersgtand IH sold the cub cadet to mdt. I do see the difference in the front wheels.

Hi,
I believe there are some differences, though I think the major one is the engine brand. See this link for a breakdown:
OEM Parts
Peace,
Clarke
PS Try the MTD model # 12AS979O100 ( that is the letter "O" before the 100.) You ca get the manual at the MTD Archive at:http://manuals.mtdproducts.com/mtd/Public.do
Just use a 1 for the serial number