How are you guys mounting rear bags

[ProudSoul]

Trying to figure out how to mount some dominator 2600 in the rear of my 63. I thought it would be as simple as drilling 3 holes in the frame but now my question is whether the air fitting hole for the d2600 will even fit as there's that funky piece of metal riveted to the frame that wraps around the back.

Picture I found online of what looks like a 2600 bag on a c10, not sure if they cut that piece off the back side of the frame for clearance or better access


I am considering buying the metal cups that allow you to mount the bag using the existing spring bolt hole but don't want to spend 60 bucks if I don't have to.

Here's an example I found on here of the cups


I bought 4 inch bolts today to mount the bag to the trailing arm and get some measurements tomorrow.

Any help would be appreciated, I have yet to find a backside view of bags mounted to the frame.