Agree, 129W footprint doesn't favor PR.
But here's what I did.(make initial measurement with dish mounted 'normal'.
1) Tie a weight on a string long enough to span the vertical face of the dish.
2) Tape it to the top of the dish hanging over it the face.
3) Adjust the dish elevation so the string just touches the lower lip.
Dish face is now straight up and down.
4) Read the elevation scale. (That's the offset)
5) Double that reading and add the required elevation.
6) Invert dish only. Not the elevation mount. (Maybe that's not possible?)
7) Set elevation scale to what was calculated in 5
Granted it's not 100% accurate as there's the accuracy of the elevation scales and 'fat fingers' but will get you in the ballpark. (No mathematical 'exactness' and no specialized tools required.) Should get you close enough to proceed with general offset dish alignment.
I had 30W tuned up in under 30 minutes with an inverted dish using this procedure..
Give it a shot, think you'll find that this works.
One night I walked home very late and fell asleep in somebody's satellite dish.My dreams were showing up on TV's all over the world. -- Steven Wright
Openbox S9, Pansat 3500SD, 139w to 55.5W +30W
10Ft USS Steel BUD and an assortment of ChannelMaster dishes, (1)84e, (2).7m, (2)1.2m,(1)1.0M, (1)2.4m[8ft] offset in storage.