Blue Z brakes

Hi all.  So when I got my 71 Z (12/70) last month the brakes were weak, barely working, after sitting for a few decades. Removed rusted front rotors and had them cut, rears were fine, replaced hoses. Drained old fluid, while bleeding the front brakes, I found that the MC front reservoir cylinder almost empty. Filled and bled, sure enough again, front reservoir was low..  Seems that when the Nissan dealer replaced the M/C back in 1986, they used the newer style. However they didn’t swap the lines.. Pedal still had little pressure, only the rears seem to be grabbing, very spongy. Guess it’s time for a replacement. 

Am looking to keep everything as original as possible. So what’s the best M/C replacement option, since old style is NLA? 

Also my leaking booster is in need of a rebuild, but am only seeing 7” rebuild kits, according to the FSM mine is a 6” booster, is the correct kit available anywhere? Thanks.