That ain't so bad, I've seen them start out way worse. It all really depends on how deep you want to get into the project. It will clean up pretty quick. Look into bead blasting and powdercoating the frame if you can afford it. It will make a world of difference and be very durable and lasting. The 70s are a simple trike that can come together pretty quickly. Have fun.
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