This is why they made aftermarket frames years ago. Stamped steel frames are just not as sturdy as a steel tube frame or chromoly frame. I highly recommend aftermarket frames. Even a ratty aftermarket frame is sturdier than a nice stock frame. It's also why honda made tube frames for their newer and bigger trikes, and they aren't even the sturdiest of frames, but they are way better than the stamped steel frames.
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