Just finishing up a 505 on a BBK. This has been a collaboration with Frank Wells, a smith of some renown with several BBK rifles in his portfolio. The action I started with was set up for the standard H&H case requiring a bit of work to function with the 505, but, as you state, it is large enough in all dimensions to accomodate the 505. The action does not have a bolt anti bind feature but it's straight forward to install a M98 type bolt guide, which I did. Requires broaching a groove in the rear ring and milling the bolt for the guide. The magazine is JUST deep enough for 3 rounds of 505 so my rifle has a drop floor plate for added space much like the Westley Mausers from the 1950s. Looks clunkey unless you like clunkey...since W/R used it, I like clunkey. I think you have a good basis for a nice rifle.

Otto