Fair point Rob, but it's not really comparing like with like is it? The Mk1 and 2 fore-ends were converted to make them suitable for the L42. The rear of the Mk2 fore-ends were converted back (to Mk1 spec - and done badly at that.....) simply to enable the plentiful existing stocks of Mk2 fore-ends to be readily utilised.
I think I mentioned it earlier; but when the dire* state of the Mk1 and Mk2 fore-end conversions soon became apparent there was a suggestion that the L39 type Mk2 fore-ends could easily be utilised on the Mk1 bodied L42 rifles. This was rejected by '.....those wot know best.....' because laterally, the open rear end was not supported by the Mk1 body - as it is with the trigger block on the Mk1/2,3 and 2. It would have meant....... Anyway it was rejected.
When we dovetail patched and pegged the muzzle ends of the L42 fore-ends (even the 'new' ones came in from Ordnance as thin and flimsy and about to break.....) we made sure that we didn't follow the internal line of the fore-end. The groove for the barrel was floated out so as to leave .020" or the thickness of a piece of card around the free floating barrel. That was all that was required so you were left with substantial meat at the tip of the fore-end
However, it was permitted to use the more plentiful Mk2 fore-ends on all marks of DP rifle where such niceties didn't matter
* I use the word 'dire' simply because there are no words to really describe the true state of them!