disc brakes
I put discs on the front of my 49 F1. I used the basic kit from Engineered Components (ECI) which came with the bracket for the caliper, hardware, and spindle adapter sleeves. The kits cost right around $100. The kit calls for using 73-90 F-150 brake rotors and inner bearings and seals, mid 70's GM mid sized car outer bearings and calipers.
Bobby
Has a complete kit with a power booster for $700.00 for a 48 - 52 Ford they may fit the Merc (he he he)

But they also have just the basic kits and they use 5 on 4 3/4 and or 5 on 5 1/2
Street Rod & Restoration Parts - Horton Hot Rod Parts
ECI Early Disc Brake Conversion Kits
It looks has if the price has gone up considerabley since I bought mine. I think I paid $110 for the basic kit...now its $160.
The GM parts used were for what GM refers to as the "A" bodies (I think) Chevelles, Monte Carlos, etc. The calipers were from the full sized cars Caprices, Delta 88's, etc.
You might try checking all the basic hot rod suppliers for disc brake kits. Next time you are at the store pick up any of the magazines geared towards classic trucks, hot rods, or street rods. They all have tons of ads from a variety of places offering these parts where you can get websites and catalogs. Also check the vendor list on this site for sites as well.
Here's a link to Classic Performance Products;
Classic Ford Truck Parts-1948-1964 Parts. The Finest in Suspension, Brakes, Steering and Accessories.
(basic kit....$95)
Concourse Parts;
Concours Parts - Wiper Motor Kits
Master Power Brakes;
Buy Front Disc Brakes & Suspensions - Master Power Brake Products
Speedway Motors;
http://www.speedwaymotors.com/street-rod-disc-brake-kits.html?category|category_root|225=Street%20Rod& category|cat_225|271=Brakes&category|cat_271|351=D isc%20Brake%20Kits
The mastery cylinder is a whole different issue depending on if you are going to keep it under the floor boards as original or if you are going to move it up tothe firewall. There are numerous kits for both locations. In my case since I removed teh stock tranny crossmember when I put my big Caddy engine in place I fabricated my own hanging pedal assy on the firewall. I fabricated it so that it connects the firewall, dashboard, and steering column. My master cylinder is fram an early 80's Cadillac, my power booster is from a mid 90's Ford Focus.
Bobby









