The bottom plate on my two piece on a classic measures 5.58” including the hinge and 4.5” for just the plate. First measurement includes all of the bottom plate assembly hinge and screw tab overall length. As far as I understand it there was only one action length prior to 64 and two after. Short and long. Differences between the standard long action.473 base and magnum lengths is all done with bolt stops and magazine filler blocks. I just looked again for the spare LA 2 piece bottom metal I thought I had but I must have given it away already.