blue27 was making atc70 suspension triples. I believe he was making custom stems for them as well. He has run drum brakes and disc brakes on his front ends. The stock 70 stem will probably not work as the lower triple on the stock atc70 fork is kind of thin and you may not have enough threads left once you mount the stock 70 stem in a "thicker" lower custom triple tree. You would probably have to have a custom stem made as well. You could always contact blue27 and see what he has done or what he could hook you up with. He's a great guy and has helped me on my trikes more times than I can count.
Nicholson 500x (Project)
Nicholson 185s
Nicholson 110 (That takes an atc70 tank)
Ascott 500 head/350x (Project)
Homebuilt Racer Chromoly Suspension 110 (Ragin Runt)
PK Racing Suspension 70
A+ Inc Suspension 70
AWS Aluminum 90 frame
Hi Performance ATC Suspension frame rd350
Hi Performance ATC Suspension frame 90