Yes, they are the same engine and there's only one Workshop Manual for the carb 308's. It's titled as a 308 GT4 manual, but sub-titled: "Also covers 1976-79 308 GTB/GTS models".
Tensioner bearings should automatically be changed when installing new timing belts. You must check your car's service history to see when this was done, but to be on the safe side, belts and tensioners every 4-5 years or 30,000 miles...