I think Joe 's car has been on the road with the RMS setup for at least several years, with a bunch of road miles on the setup.
If anything was amiss with RMS's setup, Joe would have experienced problems by now.
I have a matching numbers 1971 340 Duster and even with that type of an original car, I'm seriously considering moving to the RMS setup, for all the advantages that Joe cited.
RMS stands behind their work, and I recall that some members on the Moparts board may actually be using the RMS setup for autocrossing with excellent results.
As far as costs, if you itemize the costs for updating a SBP A body, to LBP factory stuff, you will be ahead cost-wise with the factory LBP conversion, but not by a lot, if you consider swapping out the steering box and updating all the steering/suspension pieces with top shelf, high quality components.
High quality Suspension parts are not that cheap, and if going through this hassle, remember you want pro quality components like Spicer Pro, not just any old foreign sourced low price kit from a vendor. You have to factor in, you will be installing all new suspension components, i.e. ball joints, bushings, tie rods, control arms, perhaps torsion bars and all the LBP brake parts. A buddy of mine kept a precise accounting of all the expenses, in Excel and it was a lot more than I expected.
No failures or catastrophes reported since RMS made the setup available 3-4 years ago.
It's a proven setup...