I am upgrading the braking system on my 68 Coronet. It has factory manual 4 wheel drums. I am purchasing kits from Summit for front and rear disc, that do not come with a master cylinder. I am pretty sure since I'm going from drum/drum to disc/disc no proportioning valve is needed. My current master cylinder is only a year old, but I am assuming it won't work so well. Does anybody know exactly what I need?

Thanks!

Can you find out the bore size of yours? You might try it as is since it is pretty new. Take off the lines from it & push a drill bit deep into the brass cones & you'll feel the springy rpv if it has them & if so they must come out for a disc conversion. Thread a proper sized screw into each brass seat & lever it out with 2 screwdrivers. toss the rpv & reinstall the brass seat(s). Your MC might work good for your conversion & since you've got money into it I'd have to try it 1st & see for myself.

If you use the drum m/c for discs it will need to be checked often to make sure that it does not run dry as the pads wear- calipers displace more fluid than wheel cylinders. Also you gotta be careful when you squeeze the pistons back into the calipers to fit new pads- the m/c will overflow if you don't siphon some off.