Well.....
SD1 master cyl bore 0.625" (5/8) slave 0.875" (7/8) area ratio 1.96
P6 0.7" 0.875" area ratio 1.5625
P6 slave free travel is listed as 20mm,in which case the master piston must move 31.2mm. dont know P6B throwout leverage - anybody?
If same slave on an LT77 moves 20mm, the master piston must move 39.2mm. Exedy (clutch maker) say its clutch fingers should only move 9mm to disengage, which means (allowing for the leverage) the slave piston should only move 13mm. fitting an SD1 master will go close to this.
So, the SD1 will have a lighter pedal assuming the clutch load is similar, but longer travel. The solution if the difference in pedal load is an issue is to fit a 0.625 bore master cyl. These are easily found with the same threads, cheap.