The last .29 proto I recall being published was in MAN about '57, and used a Fox .29R (bathtub intake), I believe. "Fast Miler" or something like that, and I believe the designer was "Rankin" or similar. I designed and built 4ea. .29 protos of my own, all monoline. You're not going to use 2 lines, are you?
Chris Sackett published his .21 Proto "Blondie" in Model Aviation some years ago. Tom Knoppi (F2C Tom) and I wrote the .21 Proto rules, and allowed for a handicap system for using monoline, to be adjusted as required to give parity, based on experience over a season or two of use. We gave the rules to Chris, who was NASS President at the time, and the rules were then FUBAR'd to be 2 line only, so we quit work on our two planes. Well, that and Tom lost the drawings he'd made!
You know, of course, that any B T/R design is probably perfectly legal for either B Proto or .21 Proto?

Steve