Wasn't there a link to a page describing the best way to glass bed a Pre 64 rifle for accuracy here somewhere??? Could someone post it?

Should the magazine box "float" in the mortise or should it bear against the (front/back/sides)?

I would suggest floating the magazine box. I only bed a pre-64 M70 behind the recoil lug, under the action behind the recoil lug, and under the tang. I like to use an aluminum or steel tube around the center action screw to keep it from being a factor in the bedding. Everyone has their own preference and a lot depends on the stock material. Some of the walnut can be a bit soft and you may want to consider pillar bedding front and rear action screws. The whole purpose of bedding is to eliminate variables to enhance accuracy and also to keep a stock from splitting. You'll get other recommendations. Let us know what you decide and what the results are.

I bed about two inches of barrel under the chamber portion, the recoil lug and tang...I tape the sides, bottom and front of the recoil so that the only contact is on the back surface of the recoil lug...

Sometimes I bed the barrel tight, test it, if I don't lie it then I free float it back to the chamber area (2"s), try it, if that does not work then I start shimming the forend a bit at a time, if that works, I will then place a dab of glass in front of the shim...it will find a spot it likes if you do this..

The most important thing is to keep the front, sides and bottom of the recoil lug free on a pre 64 or any model 70 IMO...

Old elk hunter is correct, the center screw is useless an can only torque the action..I use a wood block there and a wood screw, but his idea sounds even better...I will have to try that.