T or Y shouldn't matter as long as there are no leaks. Vacuum is going to equalize throughout the hose and fittings. Just be sure to use a check valve at the booster inlet to keep the booster at max vacuum when the throttle is opened. The plastic piece that adapts the vac hose to the booster housing is the check valve on GM units. Resist the urge to replace it with a plain elbow. Under normal driving you might not notice if you didn't use one but if the engine stalls and you want to stop then the purpose of the check valve will become obvious, the brakes will still work but the pedal effort will increase dramatically.
Mike
