Precision 394 is the part number for the rear U joint on a 1979 Celica driveshaft. If you have the older driveshaft (white, I think), that part should work. Precision 394 is an inside snap ring U joint design. If your current U joint is outside snap rings, you'll need to try something else.
USLC keeps some parts for the older driveshafts in stock. I just ordered a new flange yoke for the rear joint and paired it with a Precision 394 U joint on my older driveshaft.
MT