I've just found some old adverts from Trapper Industries, who used to sell modified versions fitted with a dummy muzzle brake and M16 type mag for £155. They also used the action to replicate some classic designs including the M1938 Mosin Nagant carbine and Dragunov. I still have the M1938 and perhaps should have kept the other but it went as part of a clear out a few years ago as it was too big to display.
I have found 3 pages from a manual on t'net, which suggests there was something available but I wonder if the original had more pages as the manual is very basic.
Thanks for all the replies,
John