I shoot a Parker Hale Volunteer & a mate in our club shoots a P/H Whitworth (both 1978 stamped).
Initially we both fitted Pedersoli tang base extensions and mounted our vernier on them. The tang bases come with a longer tang screw but you can be trapped as later Pedersoli screws are a different pitch to P/H , so care is needed to match.
The tang bases also require a wood thread screw to help secure it to your stock.
Our experiences with these base has not been good as we were not able to lower the vernier staff sufficiently to zero at 100 m. & this included us using elevated globe foresight.
Another problem surfaced when needing to remove the barrel - the vernier sight as well as the tang base need to be independently removed which becomes a real pain.
After discussions with Lee Shaver I have fitted one of his soule sights with wood screws directly on to the stock.
My mate followed suit and fitted a different pedersoli directly to his Whitworh stock.
Not only has this helped with cleaning but we both experience marked increase in accuracy and reduction of group sizes. The sight sit 'lower' which has corrected slighting issues at closer ranges.