the four speed doesn't help especially if one is dumping the clutch from a dead stop. Any reputable shop should be able to fab and install a stop for the snubber without too much effort but then again I haven't seen the underside of the car.
The chassis engineering kits I am familiar with are not designed for high horsepower drag strip type applications.
I might suggest calling Cal tracs again and speak with their tech support as I do not understand why they wouldn't work, Obviously they do not have a "KIT" but I would think they could put something together if they were provided measurements.

On a 4 speed car that you want to use hard you should shoot for 4 to 7 degrees difference in the pinion shaft and driveshaft on the upper line, it should have a V there looking from the side Not a up side down V As far as Mopar using pinion snubbers for traction that is a myth, the original cars (1957 and on)they came in had very little clearance between the driveshaft and the driveshaft tunnels, the snubbers where put in place to keep the pinion yokes and the driveshaft end from hitting the floors under hard acceleration comig off of dirt or wet roads or ice On your deal you need a special set of leaf prings made for your car from a high performance spring company or vendor like Tri City Performance Chassis Engr. probally sold your shop a standard set of early street rod springs made for comfort, not high performance springs for high for performance driving like you need Good luck, let us know what you do to fix it, that will help a lot of others street and hot rodders on here

"Good luck, let us know what you do to fix it, that will help a lot of others street and hot rodders on here"
Well, it certainly took me long enough. Along with some other items on the list of remaining issues, I resolved the wheel hop situation and at the same time addressed any traction concerns.
I contacted Calvert Racing about their Caltracs setup and began the process of getting their product on my coupe. Initially, I was told that they didn't have a kit for my particular application, and that I would have to take measurements of the axle housing, spring, and spring perch. Later on, I was asked to provide them with photos of these components. In the photos I included a tape measure to verify dimensions.
The kit I received looked fantastic. It looked sturdy as hell, clean, and appeared to be a quality product.
I no longer have a wheel hop problem, wheel spin from dead stop is minimal, and it's hard to see. The ride is slightly stiffer, and overall has improved drivability if only slightly.

I'm impressed that you have a 241 with 300 HP
I would start with a set of adjustable shocks and if that doesn't fix it completely, then stiffen the front segment.