I'm planning something similar, but planning on removing the rear cab mounts then do a short "Z" like you did but going to the underside of the frame towards the cab, going between the top and bottom row of rivets that hold the rear cab bracket on so that the bracket can be reinstalled into those two holes (still located as before) and then simply drill those two lower holes right through the bracket and add the two other bolts.
Still, your's will be more than strong enough. People over-look the fact that when you cut BEHIND the rear suspension cross-member on coil spring trucks that most of the stress is actually AHEAD of the rear suspension cross-member. Accelerating, braking, all goes into the cross-member. Only time the rear section of frame behind the suspension cross-member sees much stress is when you are towing. Think of it as a tow-bar LOL.
Ignore the static, you are very good at what you do.
