It's the bore up kit that will be the problem. i assume you have a version 3 gearbox.
I've not seen much stock of the SHS bore up kits for a while now, I got my AUG one from gunfire.
You can probably get away with an AUG kit. The G36 has a 24.3mm airseal nozzle, the AUG is fractionally longer at 24.6mm. Nothing you can't fix with a small file.
The AUG nozzle is also stepped, This will be the killer, So you will need to check the nozzle actually goes into the hop unit. You could turn it down with a file and drill if needed.
https://gunfire.pl/product-eng-1152212769-Bore-Up-Set-for-AUG-Replicas.html
Outside of a slightly longer airseal nozzle the rest should drop straight into the G36 v3 gearbox.
The only thing I would change on those kits is the piston O-ring. The supplied one is a little slack for my tastes and doesn't stretch enough to make a solid seal (2.5x19). So I picked up a load of 2.5x20 rings to replace it. Think it cost me about £5 for 50. There a bit harder to get in but the seal is fantastic with a slightly larger ring.
Fire support also have 2 AUG kits in stock, so it might put them back in the running if they have everything else you wanted.
https://www.fire-support.co.uk/product/guarder-bore-up-cylinder-set-for-tm-aug
https://www.fire-support.co.uk/product/guarder-cylinder-enhancement-set-for-tm-aug-series
If FS have the motor and the Gearset you want then having to file 0.3mm off an airseal nozzle shouldn't prove too big of an issue. You might not need to file anything if it's feeding aright so I'd be tempted to test it first.
The AUG and G36 share the same longer tubed cylinder head. So if you are worried about that part you shouldn't be. Guarder market the AUG and G36 heads together in the same package. I've never used the Guarder bore up kits so I don't know if they would benefit from the 2.5x20 o-ring or not.
https://www.fire-support.co.uk/product/guarder-stainless-steel-bore-up-cylinder-head---augg36-only
There the only options I can think of it you are wanting a full cylinder bore up on the G36. To be able to run the longest inner barrel possible. Like I say the AUG kit will fit, but the nozzle will need adjusting or replacing. Going with a G36 bore up kit won't work because of the porting on the G36C kits.
