I know the BSquare works well with the No 4, don't know about the No1.
For the No 1 rifle. Cut off the right hand part of the charger guide. Attach bridge between the remainder of the charger guide and front of action. Fit telescope. Worked for me for hundreds of rounds.
Next step if you want a full stock. Remove top wood, shorten barrel to 20/22". Refit front sight. Shorten fore-end. Refit Nose Cap to fore-end after removing ears of the cap and shortening it from the front of bayonet lug. Fit aftermarket sling swivel as front band isn't necessary anymore. Makes for a handy fast handling pleasure to shoot rifle. Unfortunately I didn't take photos of mine before I sold it but that is what I did.
To solve the 5 round problem, mark a line around the inserted magazine, cut of the bottom part, weld/braze a bottom plate in. The cut magazine will fit flush but will still be removable. Break off the bottom leg of the magazine spring. Reinsert spring and follower. Takes 4/5 rounds then. If you don't want to cut the magazine, buy another one to alter. I had spare magazines so I had a 5 shot flush fitting magazine for my No1MkIII*. Makes the rifle look totally different.