you'll be fine with a 50...i like the Zex kit myself, for a wet system, it uses bottle pressure to adjust how much fuel it dumps...sorta eleviates the situation of over-pressurizing the bottle and not dumping enough fuel, or under pressurizing the bottle, and being pig rich. also good rule of thumb is 2* retard per 100 "shot"

the thing that usually breaks a sprayed motor besides detonation is the initial torque spike you get...the lower in the RPMs you spray, the greater this spike, and the greater the strain on the engine...so dont spray too low.

dry shot is cheaper, and probably more easily set up, but if you dont have a MAF i wouldnt recommend using one