The only way to tell for sure is to pull the trans, and do some measuring. The bearing part of the throwout should ride on the surface of the pressure plate spring, not inside. I'm assuming you have the diaphragm-type pressure plate, right? The 3-fingered Borg & Beck pressure plate would take a very different throwout bearing, but I don't remember them ever being used on a Chevy. The throwout bearing carrier should slide over the snout of the transmission with just enough clearance to allow it to slide freely, with no more than a few thousandths of clearance. The one in the pic looks like it's 1/4" or more too big.
Jerry
