Nope, that is really the regular 6P3S, closer to 20W plate dissipation.Wow. this is old...but I would add
There is a low volt vers of the 6L6 called 6L6GB if I recall. Prob closer to the 5881
Apparently there was also a 6L6 with metal case and Cyrillic L, Stalin era before the standard Soviet denominations.