Ramified, I got a lot of my parts for my '51 from Roberts Motor Parts (in MA): http://www.robertsmotorparts.com/index.html

Here's the link to some of the brake parts: http://www.robertsmotorparts.com/truck_parts.asp?Action=search&c=Trucks+%2D+Brake+Parts

I have also used Andy Bernbaum Auto Parts Inc (also in MA): http://www.oldmoparts.com/

Here's the link to the brake parts: http://www.oldmoparts.com/g.htm

I hope this helps.