There is a good thread on here for inspiration on the mkV http://www.milsurps.com/showthread.php?t=22049
The charger bridge being chopped off isn't the best but you might be able to modify a no1 mk3 bridge hand have it rivited on. The biggest potential problem is if the sight mounting ears have been chopped off too as that would require welding to replace them. Welding on a reciever is way beyond my pay grade so if that is possible or feasable is a question for people with far more knowlege than I.
EFD offer some repro mkV only parts.
The 1923 comment above was as no1 mkV's were made from 1922-24.
The BSA rifle looks like a good base for rebuilding to military spec if that takes your fancy. (and good starter project before tackling the mk V)
Please keep us up to date and post lots of photos.![]()