[Ziegelsteinfaust]

There are 2 ways to do a C-notch, and total drop depends on a couple of factors.

Some cut the frame, and weld in the C about 1/2 to 2/3's of the frame height. The higher you cut the more reinforcement you will need.

To the above. Depending on how high the bed sits above the frame in that area. Its a good idea to weld thick wall square tube there to reinforce the span.

At ride height in my opinion for a cruiser you want 2" minimum between the top of you 3rd member, and bed floor. I prefer 3" for most builds.. My 2018 uses baby soft bump stops, and would find similar. Especially if you want to run really low.

I have built a truck with just over a 1" gap between the 3rd member, and bed floor. While usually not bad. Every once in a while it would be quite the ride. We put small RE5 airbags in back along with fill caps in the bumper to fill them up with a bicycle pump.