I sold a 47.5" RDA few years back for $1400. In barrel. Purty, purty lens. Not very common.
It *CAN* be shutter mounted. Compound 5 or Ilex/Acme #5 is required.
NOT an easy job. Barrel needs to be machined down IIRC. But definitely possible.
NOT cheap(about $850 IIRC, not including cost of shutter!)
SKGrimes is the best. There are others, but I've used SKGrimes multiple times, and they do fantastic work through-and-through. No complaints whatsoever.
I know 3 people who have shutter-mounted 42" lenses(one's lens is an APO Ronar CL, the other's two are LD Artars, but same thing almost). Both used Ilex #5's for their mounting. All use the lenses on ULF(two w/ 8x20), the other with 11x14,8x20 and 12x20.
All use that FL regularly.