like the topic says and can they be retrofitted to early 120Y's?

as I have access to both...

contemplating putting the alloy rims off the sunny on "the Defect" (march '77 aussie 120Y as they don't fit on "The Iron Maiden (July '75 (japanese) 120Y as the rims foul on the calipers I contemplated trimming off/down the offending "shroud" but will wait to see if the late model calipers foul the alloy rims....

newer brakes are generally more effective at stopping, but usually are heavier.

trimming the shroud would make the caliper unsafe if you're talking about what i think you are.

They can be retrofitted to earlier 120Y's by installing the strut that they bolt to. Remember that later 120Y's used a different bore size in the master cylinder, to make the different caliper piston size do its thing properly, so you will need to have a good old think about that.
While you're at it, remember that the matching rear wheel cylinders have a different bore size too, to match up with the master cylinder that matches the discs, however, these do not interchange into the Japanese brakes, so a whole rear axle swap might be the go in order to get a balanced system.

Get a Gregories 120Y workshop manual. It has all the specs for both versions & you can start doing your homework from there.

The new brake system was used because it was available from an Australian manufacturer, as were the Armstrong struts & the Warner rear axle assembly. This was done to increase local content in the locally assembled four door sedan after July 1976, & I don't know if the brakes were any better, or just as good, but locally sourced.

i've got a '74 120y with the jap brakes and i'm running a 14inch rim which fitted fine until i put in some new brake pads, this caused the caliper assembly to be pushed further out and hit the inside of my wheel.
I choose to grind the outer edge of the caliper which seems to work fine.
I would recomend buying some wheel spacers as this should fix the problem without having to grind the caliper

okay, for the brakes, larger caliper,larger brake pad, larger disc,bolts to the stock steering arms,
brakes are very good. against the brakes - i found they wore the pad unevenly,due to an offset piston in a caliper designed for a larger disc,making it look like there is plenty of pad left on the outside while they are nearly finished & causing pad knockoff,& they dont really like stopping from about 100 mph into the stop corner at amaroo, they sort of warped the disc & caused some alarming shudder.that last one was just a personal problem,this swap was something that i always did with my street 1200's,even had a police car almost rear-end me when he pulled me up for speeding because i stopped quicker than his dumb commodore.plus you can get thirteens to fit easily,something the japanese calipers won't
allow with new pads.my advice,perfect for a street driven 1200 with even a warm a15.