Well I can quickly dispell a myth here, I have had a word with the local guy that does cylinder testing here,
Myth 1, " You can't have welded cylinders tested" Bollocks, you can't have cylinders welded back together. Different from having cylinders that are actually designed that way
Myth 2, "You can't have them tested because the idest centre can't stamp them on the neck" again bollocks, apparently they epoxy glue a stamp on them,,,,,,, as the guy explained to me, "you can't stamp the fibrous ones either"
In effect all he needs to know what the test pressure is, as Iain/HSM has pointed out, despite the age they do get a very easy life really, and if the inside hasn't been subject to anything sinister or left wide open for years it should still be good.