I have had a couple of these over the years and one of which still retained the original butt. It had been relieved to accept the Mk.III rear sling swivel mount but there was a third hole in the center from the original single lug swivel post.
There are many different variations for this conversion and I don't think there was any "set in stone" pattern for said conversions. Some rifles I have noted in the past have had all original Mk.I parts still fitted and only a lining out of the original serial number for a new ER/CR prefix one.
I have observed Mk.I forestocks having been relieved for Mk.III rear sight protectors, retaining the volley sights. I have also observed the volley sight reliefs patched with wood. A couple of examples have retained the original rear handguard, having the integral rear sight protector removed and the Mk.I forestock relived for the MK.III sight protector. I have observed Mk.III forestocks, with volley sights intact, as replacements using the original barley corn nose piece and I am sure we all have seen the retention of the Mk.I rear sight and also the use of the windage adjustable MK.III replacements.
I'm sure the above mentioned is only a small portion of the variables done but it is only what I can speak of from personal contact with them.
A good thread I think
