Hemi68, I have an A518 in my GTX that was previosly fitted when purchased. Any reasons as to not using the A518? I dont know too much about their strengths but it was bought through MP back in 96 and documented in Hotrod.I hope the A518 can handle some 1/4 mile launches
see here http://www.hotrod.com/howto/43323_mopar_overdrive_transmission_swap/index.html

Im fitting a 3.91 gear next,I just hope the A518 is strong enough?
Mine also utilises a toggle switch, no biggie , just flick at speed to engage, and flick off to re-engage 3rd gear at a reasonable low speed.

cheers Dave