I'll check the 6C4C stash, I can definitely send you two, and probably four of them. These would be the 50s vintage twin plate Svet's.
EL36 is "somewhat" similar to 6BQ6GTB/6CU6, which is, in turn, very similar to 6AV5GA in operating characteristics. It should work in triode strapped mode , probably good for 3WPC with 3K and 300V P-K - just a SWAG
IIRC, the 6BQ6 and EL36 are "pin compatible" with the Clem boards, just run the plate cap lead back to the Pin 3 (plat) pad on V2 and V3.
/ed B