Re: Picatinny rail for M77 Ruger .243
Have never used one, but I suppose if you used it, you would go with a low ring instead of a medium. One question is what height rings you currently use ? The QD maxima rings may really be the ticket, no rail to add extra height. Looks like they only come in medium and high though, perhaps not surprising when you have no rail on the receiver in the first place. I imagine that the built in mount is going to be the best aligned with the receiver that it ever could be.
Just remember that if you go with the picatinny rail converter that you then get "regular" Maxima rings, not the ones made for the Ruger 77 receiver dovetail...