Quoted:
My advice is to measure it out, and then use masking tape to get your lines square, and go slowly either with a hacksaw, or fine-toothed kerf saw.
Then dry fit the hinge, mark your screw holes for centers, and carefully drill out two holes for deep nuts/coupling nuts like these:
https://www.fastenal.com/products/details/0170895
Can't remember the depth of the coupling nuts I used, but grinding down the ends so they don't interfere with the rear of the receiver would be pretty easy if they're too long.
I set up mine to fold on the right, since I figured if I ever slung it, I'd not want the bolt charging handle to dig into my back anyway.
(edit) Sorry, forgot the rest of the build details:
Kidd Engineering 6" stainless barrel.
Kidd Engineering bolt buffer pin.
Kidd Engineering quick release bolt lock.
Kidd Engineering guide rod and spring.
Tactical Solutions long mag-release lever.
Ruger BX trigger pack.
Gemtech Outback II, sealed, not the "D" for Disassemble, but I got it at a good price from a FFL/SOT friend who had a customer bail on it. I'm sending it in to Gemtech for the $25 jailbreak/monocore upgrade though.
Original Charger knockoff Harris bipod.
Stormwerkz push button hinge assembly.
Ace AR buffer tube adapter.
PSA milspec 6 position buffer tube.
MFT Battlelink Minimalist stock.
The Bushnell Trophy red/green dot does the job, but I'm going to upgrade that sooner or later to an Aimpoint T1 style, or mini reflex sight of some kind.