Neck mounting

[XLayaR]

Hey guys, dunno if this is a common question but here goes.

Whats the usual way to calculate the required neck dimension/scale from the body? I wanna order an RG like neck but I scared my scale wrong(it'll have a locking nut and FR btw)

Also, do different necks have different mountings? Like the screw that part got any difference anot? My body is not a typical RG body and I'm afraid it wont fit in.....

Thanks in advance guys!