Maybe do another careful measure of the dovetail - both front and rear. Original Parker Hale bases came in two widths - the "A" was about 19.5 mm, and the "B" was about 16.5 mm wide. To stay original, you need the correct size rings to go with those bases. For the rear one, a correct base might be "A21" - it says that on the top face of it - a similar one that only says "Parker Hale England" is also commonly sold, but that is the narrow one - the "B" width. If it does not say "A21" on the top, it is not one. The partner base, that is drilled and tapped by two 6-48 screws onto the front receiver, needs to be similar width - so very commonly to have an "A20" front base - drilled and tapped into front receiver ring - with an "A21" rear base, which is a direct replacement into a military No. 4 - uses the same mounting hardware as does the original rear sight, including the cross axle, the plunger and its spring underneath.
For the narrower "B" series, there may have been a "B20" front base made - if so, I have never actually seen one.
Then, several heights of Parker Hale rings will "fit". That rear A21 base has a divot to receive a recoil stud from the rear scope base. The front A20 base does not have a divot, so the stud is removed from that base, if it has one. I have had a few through here that people took an angle grinder to them to remove - just tap out the cross bolt and the stud falls out. The "usual" rings that were used are Parker Hale RAHS.3 for 1" scopes - these are high enough to allow the rear aperture battle sight to remain on that A21 rear base. If you want to use lower rings, like the "N" or the "L" heights, very common to see that rear aperture sight ground off. Of the several RAHS.3 ring sets here, only one ring has the recoil stud - the partner does not. Of the several RALS.3 rings here - all have recoil studs on both rings. The cap screws are size 4BA - I had bought some via Internet from England - I had ordered 4BA size 1/2" long socket head cap screws from BA Bolts - seemed to be a perfect replacement into the Parker Hale rings. The same size bolt, except 1 1/2" long makes a perfect replacement for the clamp cross screw in the Parker Hale rings - the cross bolt heads are not all the same size on PH rings but the shaft / shank is - but those 1 1/2" socket head cap screws - size 4BA - seem to work perfectly - the thumb nut just threads right on.
