I would to thank everyone for the feed back so far.
I have thought the machining through alot. and yes the bottom rib in the form presented makes machining very difficult. but keeping with the DIY theme i'd already figoured somthing out. the nice edges look prettier though.
I admit my paintbrush or sketch up drawing arnt 100% of what it will end up looking like.
so here is my solution to the bottom of channels.
place the block on its side and drill straight down.