Synchro's is short for synchronizer gears. I'm too lazy to type all that out.

Synchronizers are bronze rings which are cut to match the ends of the actual gears. They are tapered on the outside edges which enables the shifting forks to "slip" the hardened metal gears and allows them to mesh smoothly or synchronize the speed of the input shaft to the main shaft when you change the gearing. Yeah, yeah, I know, more than you wanted to know but you asked.

I bought an old rust bucket for $150, pulled the tranny and crushed the car.

If you go the crusher route, pull the clutch pedal mounting bracket and all the related hardware. You can sell that stuff for usually at least as much as you paid for the car. It is what is needed to do an automatic to 4 speed conversion.