Kev, remember this when you go to install the countergear.
Press the bearing towards the front of the trans on first and then put the countergear inside the case. When it's in the case, then press the rear bearing on.
Some publications say to press both on first and then insert it in the case. This only works with certain gearsets. Not all will fit this way. To be safe, press the rear bearing in after you get the gear in place.
BTW, T-5 bearings are standard bearing sizes. You could go to a parts store and buy new ones if you have the numbers. I beleive the last one i built i used Federal Mogul bearings and have the numbers somewhere.