I admire your pride in your work! rare these days.Agree with the above. and I will add that you REALLY, REALLY need to do it on a milling machine for close tolerance and good finish. drill presses are ok, and will get the job done eventually, but they're no where near the precision of a Milling machine.
There are some youtube vids out there that make me cringe and wonder how they haven't lost a finger yet...
Im pretty quick doing them and with the manual mill, i can get thru one in about 3 hours. Im very anal about my work and finish so I do take a hair longer addressing the little things.
there are a few tight, or absolute measurements that you have to take care with, but most of the work is hogging out all the excess.
Then slowly finishing the outside edges of the cavity to the correct measurements. and drilling the pin holes in the correct location using the proper bits.
Most jigs out there will work for 99% of the mil spec receivers on the market. the only time you gotta be careful is with oddball shape and cut billet custom stuff.. thats where you will get into issues with proper fit in the jig.
Modulus Arms Jigs are actually pretty nice quality actually and I cannot say anything bad about them.