Munroe's book won't show the transfer plate mods needed to build a RMVB. The pic below shows (in red) the channel partition areas that need to be removed. (1/4" cutter)

For those without a milling machine, a thick steel plate with a 1/4" hole drilled in it can be used. Place the hole over the area to be removed, clamp the steel plate to the transfer plate with two C-clamps and drill out the partitions using a 1/4" drill bit...mark the depth on the drill bit to prevent drilling too deep.