I have just updated my old coil and oil sprung forks for a nice set of air and Ti spring Marzocchi 44s.
I have an ultra reliable set of 4pot Shimano XT which have given me no grief whatsoever over the last 7 or possibly 8 years.
Do you think I could find an adaptor for that set up? Well, yes eventually. What a palava.
There isnt a bike shop in England that seems to know what I am on about and give me that "you don't know what you are talking about old man!" Look.
Finally I spoke to windwave who have given me a part number which I will need to order from a local bike shop.
Ok so Shimano XT 755 4pot disc brakes are IS International Standard.
The Fork is Post Mount.
You need an A2Z ADPMF74 adaptor but need to upsize your rotor from 160mm to 180mm.
Comprende Amigo?
Si Senor! 
Should have asked the STW massive - we'd have pointed you to that adaptor in about 10 seconds. 😛
Theres a KCNC adaptor which means you don't need to change to rotor size either.
Did I imagine it or did shimano do an IS to post 160-170mm adapter at one point also?
I've got some IS mount XTR calipers which I'm not changing as they work perfectly I think if I switch to some more current forks I may well be in a similar boat and will probably just have to up the front rotor to 180mm...
A Hope IS to post mount +20 also works in conjunction with a 180mm rotor too.
Also Shimano do/did an IS to Post mount adapter for use with a 203mm rotor too. I have one of these spare if you want it...
And yes, always ask on here first... Saves much grief IME!
Hope did the 170mm adaptor for old Manitou forks, still got one in the spares box. Another, probably more readily available, option is the Hope HBSM20H mount.