I agree with other posters on the first year dual masters were installed and why (a change in FMVSS - Federal Motor Vehicle Safety Standards). On a '61 Lancer or Valiant you can bolt the '67 and later distribution block on your car in the same location as the original was mounted, though you may have to drill a hole in the frame rail for the alignment tab on the later distribution block bracket as they are located differently from the '60-'61's (For '62's it's a direct bolt on). The rear brake line will screw right into the later distribution block hole. The lines to the front wheels have to have the fitting at the distribution block changed as they are a larger thread than the originals. If '61 is like '60, and the right front brake line crosses over by going forward and crossing over under the core support you'll need to extend it (or remake it) to attach it to the distribution block if mounted in the stock '61 location. The alternative is to mount the distribution block forward so the stock length right front line reaches and extend the rear wheel line to meet it. After doing several of these my opinion is it's easier to mount the block where the rear line reaches and modify the fronts to fit. If your '61 has the firewall mounted line to the right front wheel it can be rebent and reused after changing the fitting mentioned earlier if you've mounted the later distribution block in or near the original location. I always buy the left front line off the donor car when I buy the later distribution blocks because it already has the correct fitting and is easily re-bent to fit. I also will cut the right front line leaving the fitting I need in the donor distribution block.
On the brake light switch I usually convert to a '62 style electric (still readily available on Ebay). It is labor intensive since I pull out the pedal support to drill and slot the holes for it. Also helpful if the instrument cluster is removed so you can find and extend the original wires to it. This is more difficult on Lancer's than Valiant's because removing the cluster does not give the same unfettered access to the light switch due to the dash pod bezel design but still helps. The '61 light switch has a constant power terminal (10/24? thread) that is close for powering up the switch, but there are any number of other hot wires to tap into. If going hydraulic tap into any line with a "t" fitting and extend the factory wiring.
Brake pedal rod length is either the same or so close I've never noticed a difference. You can buy a manual brake dual master with the rod or a power brake one without and use your '61 rod after removing it from the old master cylinder. No right or wrong here. Unlike disk brakes manual drums and power drums use the same master cylinder piston size from the factory.
clear as mud?? Feel free to Pm if I can be of additional assistance.
