Four inch drop coil spring question

[Wootdog]

All,
I have been thinking of installing some four inch drop springs on the rear of my 67 C10. A couple questions come to mind. Do you have to C Notch the rear for a four inch drop? Back ground the truck has a narrowed nine inch Ford rearend with discs. It has a beefy sway bar setup that is in the way of the original location of the springs. I am thinking of taking that sway bar out. I already have bags but that has caused some problems in the past. When the rear was setup, additional metal was installed to the inside of the trailing arms. This was for the cups the bags would set in. I found out the hard way that this was not done right. When air is put in the bags, the trailing arms flex downward which caused the axle to slam into the frame which in turn caused the axle housing to fail. I have since had a shop putting the axles and third member in a narrowed F150 housing. They stated that if I wanted to get the rear right, I have to C Notch the frame. I would like to just install four inch drop springs on the rear trailing arms in the original location. I am over the air bag setup. I had been using the bags like you would for air shocks. I never acquired the rest of the setup due to money constraints. Any suggestions would be appreciated. This if the C Notch is done will be expensive.
Thanks,
Kerry