Your explanation of the function does not convince me that the channel needs to be round.
If it does not, then a very cheap design where two hardened 3/8" thick strips,shimmed for clearance, lie on top of a heavy bar, a hair over 3/8" apart. On top of them lie two slightly wider hardened strips with a little over 5/16" between them. All strips are punched, top strips are csunk, for securement to underlying heavy bar every 6" or so with flat-head screws.
Cheaper to make, longer wear-life, cheap overhaul when worn.