Black Rose Baby build question

[SBJ]

Some months ago, I bought an NOS Framus Black Rose Baby mandolin neck because I like the black and red vibe and the pearloid headstock. I'm building an A5 style body for it with cats eye f holes, black top, sides, and back, white binding, and possibly an understated red sunburst, although it won't be as deep as the original. The shape of the heel seems to dictate attaching the neck with either barrel nuts or threaded inserts. I would reinforce the threaded insert with a vertical dowel and epoxy as Graham McDonald recommends. The question is whether there's room for one or two bolts. The heel is 36 mm high and tapers from 24 mm wide at the bottom to 34 mm at the top. It is at least 32 mm thick horizontally where the bolts would be installed. The heel will fit into a mortise formed by the ends of the sides, and I'll access the bolts with a long hex wrench through the tail block. The neck angle is about 2.5° which is low but appears to work. The fretboard extension floats above the top. Any comments will be appreciated.

[Graham McDonald]

I would be thinking about M4 threaded inserts rather than the larger 6mm type used for guitars. The vertical dowel in the heel is a good idea for a couple of reasons. Many German mandolins of that period used a half grafted heel. The neck shaft and head were cut from a piece of wood around 1.5" thick and an extra piece glued on the heel end to make up the full depth. It looks like one of them in your photo. This glue joint often fails, leaving the lower part of the heel glued in the mortice and the rest of the neck pulled up. The second reason is that it can be very tricky to get a threaded insert into end-grain maple without it chipping out. The Black Rose baby's were a very cool mandolin