I did this by splitting the neck wood in half then bonding each half on either side of the aluminum, I varied from traditional adhesives used in banjo building and went with a polyurethane glue. The glue used was Gorilla glue that they sell almost everywhere these days.
Using an orbital sander, with 60 grit paper, I scored the aluminum to get a good bond. After scoring, I cleaned the aluminum with lacquer thinner and damped the wood just before applying the adhesive. Dampening the wood will aid the polyurethane glue to cure more evenly.
My theory was I could grind the neck flat before finishing the fret board and the neck would always stay flat due to the aluminum sparr. It would also leave a unique aluminum stipe down the back of the neck (coolness factor)
Notice all five peg holes in the peg head. I don’t like working around that peg on the neck when I play. The grove is to bond a brass tube beneath the fret board for submarining the 5th string.
I will add more soon.
But just for a note: I thought that sparring the neck was innovative and all me. I later found out that Martin Guitars often bonds a square tube beneath the fret board for just the same reason. But they didn’t get the cool aluminum stripe.