How much horsepower can an L52 trans handle? Dropping a 302 in my 83 2wd and can't find a t5 trans right now

 

It depends.
They have two major strong points: the cast-iron case and straight-cut gears, I've heard from a few mechanics that they're some of the toughest gears used in a Toyota pickup.
The big weakness is the input bearing. The first run of these transmissions had the same bearings as an L42, and were tiny and prone to failure. Later L52s had the same bearing as the G52 and W56 (you can even verify the part numbers).

Bench racing here, I'd say that a well-built L52 with the larger bearing could handle the same abuse as a W56 or G52, possibly more due to the gears and housing. If the transmission is already out of the vehicle, it would be wise to have a new bearing and seal installed.