I had to scratch build a bracket to mount it all, using the lugs off the airsoft unit.
It slots together and the recoil unit is secured with a tiger track pin (top hole) and a screw in each side
It all fits in the turret rather snugly
It all felt a bit loose so I added a bit of tubing (an old ariel) to each lug so now the gun doesn't wiggle about.
One thing I've learnt when scratch building stuff is that it's easy to make things look good and work properly, the hard part is doing both of those and make it servicable.
The first tank I rebuilt worked great until one day something broke and I had to tear it apart to fix it.