There are (or were?) shops that rebuilt old shocks (spiral), but I can not attest to their quality after rebuild...?
This is the only one a 'google' turned up...
http://dansshocks.com/shock-rebuilding/But I also found some information I wasn't aware of on a Corvair site. Following are two posts from a fella on that site:
1. FYI, straight from the Delco engr. The spiral is in the outer tube which is the reservoir for the fluid. The inner tube contains the shock piston. The spiral was used to prevent the fluid from from becoming airated from sloshing around. Previously there was a baffle in the middle of the reservoir to accomplish this. The spiral was easier than the the baffle to build into the shock. Haven't heard from the person who was going to rebuild them. Jim
2. The former Delco engineer I know is not rebuilding spiral shocks at this time. Too busy with other things. Possibly some time in the future. To rebuild them one has to cut off the top of the shock, fix the stuff inside and reweld the top back on. Not easy. Jim