slingslingbinks, well I'm sorry to tell you but I've never seen a replacement seal for the rope one. I've built a few Pontiacs in my time, 326, 389, & 421 ...they all used the rope seal. Actually it's not a bad sealing method either! Afew tricks to use, be sure the rope channels are clean! Take a coal chisel and but some "dings" in the channel (this helps from spinning the seal). Try to get a solid piece of wood or pipe about the same diameter as the crank journal and use a rubber mallet to "seat" the rope in the channel. Use a razor to cut the rope ends flush & clean, then use some silicon sealer on the rope ends.
It's not a hard job if done correctly, and will last as long as any factory seal ...in my experience. Just don't complicate the issue by trying to do this with the car jacked up, pan off, and just the rear bearing block off. ...And maybe flat on your back!!? ...It may be a "pain" to pull the engine, but remember the old adage ..."Never enough time to do it right, but aways enough time to do it over!" Truer words were never spoken! ...Again, in my experience, Good Luck to you Sir. ...Mark