Homebrew PCBs

So as I stated in a previous post, I have acquired some vintage 1973 PCB
stock, which is perfect for a project I'm doing that replicates the 1973 TV
Typewriter.  Except for one thing - the stock is 0.31" thick, rather than
0.625".  So my thought was to epoxy two pieces together.  And that works,
except despite my best efforts, I end up with these ugly voids you can see.
I've tried putting the boards under a press with heavy pressure but there's
always a few spots.

 

Is there a better way/adhesive to do this?  

 

I realize it'd be easier to use 0.625" stock from the outset, but stock of
the correct vintage just isn't available, and it means a lot of me to be
using actual boards from the time.

 

Thanks!!