Skip the 650b conversion. Most opinions haven't taken into account the extra 15mm of tire (38mm vs 23) - it won't fit. Put a nice light set of mtb wheels on it. It's a common trick to get fatter tires on a recumbent designed for 650c. The brakes "should" work, you'll have more tire clearance (not less), and there are lots of wide, fast 26" tires out there (the Schwalbe Kojak 26x1.35 is my fave).

SP
Bend, OR