So, I finally got around to doing something with the new R4S pads...from a year ago.
The front FRP-105 were 0.848" new in the box. I needed to cut them down to 19mm or approx 0.750" to fit my calipers.
The new rear GD557 fit without any modification.
As usual, Peter H. was correct and his info on these options is still valid.
Regarding the R4S, I feel they are good street pads but not made for track use. I will keep my very effective but heavy dusting track pads for more serious situations.
As an aside, my car has stainless lines and modern racing brake fluid. Combined with new modern tires, it stops extremely well.
A modern supercar snob friend of mine exclaimed when he hit the brakes from 100mph.
Not bad for a 40yr old car...
LS