Well, so much to review...
You do not have to press mag support dimples in your home rolled receiver. The new RPK-74 does not have them. The rails you can get from SKSMAN have sufficient "meat" to support the mag. Be careful tigging in the rails. You can overheat them and loose the temper. Then your ejector will peen like a soft nail. Someone reported using screws to install his rails. Just another option...
Heat treat is a hit or miss thing. It is almost impossible to do without a furnace. Using a oxy/acet torch is a waste of time. Half of your receiver will be molten, half cold, and the oxide scale will be too thick to successfully remove without a hammer, which will destroy the receiver. Don't even try that method. Also, once you get it hot, you have about 3/4 of a second to quench it. The thin sheet metal will cool past the transformation range in air very quickly. You need to "shock" it to get any hardness at all. There are two up's to this. #1. you can test your technique on some scrap pieces till you get it right. #2. If you blow it, you can anneal it and try again. DO NOT weld in the rails BEFORE you treat the receiver! Do not quench in oil. 4130 will not harden like 4140. You will have to use extreme quench techniques (water)to get any hardness at all. Also, if you quench in oil, forget about black oxide. You will never get the oil out of the pores in the steel, and the oxide solution will bead up and roll off.
A ceramics kiln is a great heat treat furnace. You need to go slightly over 1650 F. There will be considerable scale oxidation if you leave it in very long. I've had luck with a five minute soak. So heat the kiln before you put in your metal. Have your water quench even in height with the top of the kiln so you can pull out the receiver and quench it in 1/2 second. I use a piece of coat-hanger wire run thru a hole in the receiver. Remember, the wire will be more like string than wire at elevated temperatures. Use welding gloves and KEEP YOU FACE FROM OVER THE KILN. If you've been successful, the receiver will "ring" when you tap it. If you did it wrong, it will go "Phlud".
That about covers home heat treat. One additional thing worth mentioning is that heat treat will cause slight warpage so the thinner the sheet metal, the less spring pressure the screws will have to overcome to hold it square again. I destroyed 18 receivers learning how to do this correctly, so I'm speaking from wretched experience, not hopeful speculation.
Good luck.