First, any members with this information handy?

Secondly,where would a guy buy a factory mag box, follower, and spring.
Thank you!

Internal overall length is usually close to 3.650. Mag box, spring and follower are available from numerous vendors like Midway, brownells, numrich.

I have one in the parts drawer I can measure, but off the top of my head I can tell you it is the same overall dimensions as the standard long action box but with cut outs on both sides. I ordered mine a few years back from Brownells. Follower too.

Thank you for the magazine box sources.I'm still interested in an actual measurement though.Thank you.

Found magazine box, spring, & follower at Brownell's and Midway. I know I'm on track the box and the follower because they reference Ultra Mag. Would I just use a long action, BDL, magazine spring?

The magazine spring is the same. You may need to tweak it to feed flawlessly but that's it.