Yes some 54 and all 55 and up 261s I believe will /can have a neoprene seal. I just finished a 261 rebuild and assembly myself, used the neoprene and it is dry as a bone under there, if you can use the rubber seal use it over the rope in my opinion.

Last edited by sstock; 08/08/2019 6:01 PM.
1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration