My friend has an SC400 and he got a aftermarket torque converter. IDK what it is I just know it is purple. He says that he will sell it to me but IDK if it will fit into my SC300. Info would be much helpful.

A Torque Converter is basically the clutch of an automatic transmission. If it is purple then that means it is the Dragon Torque Converter, one of the best you can get for the SC. Unfortunately I do not know whether if will fit into the SC3. I don't think so though, since the engine and drivetrain are quite different. Maybe the DragonTC for the Supra will work for you.

Is there any why that I can find out for sure if that torque converter will work on my 300?

I have emailed Precision Industries (the maker of the purple torque converter) in regard to this same issue when I have seen these units for sale on the classifieds. The SC300, SC400, and Supra TT torque converters are all different and are not cross-compatible.