https://www.bopengineering.com/olds_v8.shtml bottom of page the seals supplied in the newer gasket sets use a government mandated non graphite/asbestos seal that is difficult to install and leaks. If you want rope seal get a NOS gasket set made before 1995.
Would think you could use a 2 piece rubber seal. I used one in my 54 322 Nailhead, got rid of the new/leaking rope seal, it works great. Russ Martin sells them for Buicks, he also supports vintage Caddy engines, wouldn't hurt to give him a call. http://nailheadbuick.com/caddyhotrodparts
I would contact Tony at Ross Racing Engines, he's the go to guy for most Olds questions. I'm sure he has an answer for you. Ross Racing Engines 1763 North Main St Niles,Ohio 44446 330-544-4466 w 330-720-1282 c www.RossRacingEngines.com