KH disk front 83/4 rear, prop valve and master cylinder brake line question

Yes A larger resevoir is recommended because as the pads wear, the piston starting positions move outward.
A couple routes you can follow:
Pre-67
https://www.web.imperialclub.info/Repair/Lit/Master/219/Page06.htm
Or '67 up tandem Master,
https://www.web.imperialclub.info/Repair/Lit/Master/233/page13.htm
For the pre-'67 set up, you must the proportioning valve in the feed to the rear line.
https://www.web.imperialclub.info/Repair/Lit/Master/274/page08.htmWith the tandem master you can use the prop valve in the rear line, or a combination valve as was used by the factory 70-72.
However the '65 AFAIK has no provision for the brake failure indicator to connect to a 'safety switch'.

https://www.web.imperialclub.info/Repair/Lit/Master/index.htm