Outer Limits 4x4 Board

hey guys,

just a quick one, i have a 45 series with disc brakes up front and drums on the rear, i currently building mine and am ready to purchase the parts for my brakes.
now i have the twin cylinder on the rear and from what i hear using these, will lock up the rear of the truck very quickly. to overcome this i was going to put the smalle bore brake cylinders in. does anyone know what model the smaller bore brake cylinders came out in??? if tried repco and the like but they only have part numbers,

cheers guys,

You can use the entire drum/backing plates from a 60 or 75 which will also convert the handbrake to the rear drums.