Using the MGZ series optics for indirect fire of small-arms ammo requires nothing more than what we used for Mortars....or Field-Artillery in the US Army.
1: Required equipment:
A: Aiming-Circle or even an M2 Compass for direction.
B: MGZ series Optics mounted on the Lafette.
C: Collimator mounted on the head of the MGZ series Optics.
D: Map of your location....required to compute data (for direction/Azmuth) to set on Aiming-Circle/M2 Compass (RK31) and to comput data for Optics.
E: Aiming-stakes (what you may be calling ranging-stakes) for use as an aiming-point...but you can use any DAP ("Distant-Aiming-Point") that is in view from the optics that is at least 2,500 meters away.
F: Range-Tables......that book (or sheet) for the ammo that you will be firing that says what the elevation (angle of gun barrel) will be set on the Optics-elevation-scale.
2: Nice-to have-equipment/information:
A: Known range/ballistic data for the "LOT" of ammo you will be firing.
B: Corrections for elevation with this ammo.
C: Corrections for "traverse" of the gun for wind/temp., etc..
D: If the gun was "Bore-sighted" on this Lafette ?.....and if the Optics being used were bore-sighted/zeroed.......there are two methods for this......using a fold-out chart as in "Folke's" book........and/or using that DAP (over 2,500 meters away).
The RK31 (?) should have a scale of 6400 mils around it if it is set up as an aiming-circle.......it should also have "level-vials" for setting it up level....and the magnetic-compass inside of it should work (but may have a lever to lock/release it.
"Mils" are more accurate as there are 6,400 "Mils" in a circle...but only 360 degrees in a circle.
Let me know what you have....and if you are interested in learning "Indirect-Fire".
Note: This could turn into a long thread if required subjects have to be covered so that everyone knows how each piece of equipment is used, teminology, and then the "set-up"....math for computation...and that we will need some Balistic-data for 8x57mm ammunition (IE: At _____elevation of the barrel ....the bullet will travel ______meters. These are kind of like charts in their basic-form.