1st hope that the barrel is 8mm and not drilled.
2nd """Where's the schematics to do this?""" go the the mg42 area and review what is there, what you need is there. The Lobo 1919 build stuff on this website is either Pirate's work or Oakrodent's work mg42 /m53 work. Look for their threads.
3rd plan on getting a brp rear to weld together and attach to your barrel shroud as you are lucky enough in that you got a camming area that can work with a brp rear.
http://www.brpguns.com/
4th read read read then ask a few more questions as several new folks on the site either just finished or are building one at this time.
5th Plan on buying John Baum's German books. They are to the mg42/m53 as kkkriverrats books are to the 1919....
http://www.germanmanuals.com/ email him and ask which ones to start with.
6th Pirate and brp have semi stuff. There are several others also doing it. However you can do this yourself also. Review the stuff on this website. brp sells a ready to go bolt and/or also the parts to redo things yourself. brp website also has several nice diagrams that will help.
7th Also quit searching the net.... You are here now.... This is the place with the info like 1919a4.com is for 1919 well mg42.us is for mg42/m53's
Good Luck and ask more questions after you have reviewed the 5 - MG42 topic areas and used your search button.
Later 42rocker