New brake hose is a must on these old Airheads. The originals have all swelled up and choked the hole down the centre by now.
And that rear brake is a bitch to bleed for some reason. Taking caliper off and hanging it so rubber hose is vertical helps, as does a vacuum bleeder.
Can't remember exactly but I think there were two sizes of master cyl bore, the later ones being smaller and more effective. You can get the old ones sleeved to fit the later piston/seal.
'77 Harley Ironhead 6,000 miles across Oz
Reryder (AKA Hopper)
1977 Harley Sportster
01 HONDA VFR800
Ancient Harley 45, Snortster (Sporty engine in a Norton), Norton Atlas, Honda 350/4, Ariel HS scrambler