Hi H2W, thanks for chiming in.
The later caps do indeed get me within spec - 7mm from washer to cylinder.
Okay, I don't need to be told a third time not to spend money
. If you both think the longer caps are good enough, I'll just run them. I've read around a bit more and had a look at somediagrams and by the looks of things the early tensioner were just overly conservative in their tolerances.
I'll let you know how loud the bang is when it grenades :P
Thanks for the help.