A thread on ADV Rider was enlightening; describing only a possible 1-2% increase in braking performance. Snowbum's site listed all parts but some of his part numbers are no longer accurate. I'm now thinking my current lash up, which is working well with twin, braided SS hoses, may be just fine as is.
Funnily enough that was what I came up with the last time the under tank M/C annoyed me - lots of cost and no advantage. I have the under tank M/C stainless steel sleeved and threw yet another seal kit at it - was working perfectly when I parked the R100.
I also agree that the biggest upgrade you can do with SS ATE calipers is fit better quality lines.
I was always "going to get around" to upgrading the brakes, the funny thing was that as the bike and I got older I went less hard and didn't need upgraded brakes. Then originality was worth more than any braking gain....
But, I've since discovered that the 1980 on fork lowers will bolt straight on, which raises the possiblity of fittign Brembo F08s or ATE calipers. Given that the original SS ATEs are 40mm, I suspect that the smaller Brembo or ATE opposed piston calipers could be fitted without having to alter the M/C bore size. Not that I am going to do that now, I am locked into a "original" restoration for the old girl, the latest "big find" has been a brake place that has the right chemical wash/preservative to restore the pretty blue colour of the original ATEs.