The tires on this bike are 28.25" tall-700c 42-622-nominally they are 40mm 700c-ISO 42mm.They are very big for 40mm in that the carcass is roughly 41 wide and 42 tall-.
It took a bit of doing to fit this tire.I have-had-a french frame that would accept these tires by just shaving the tire lugs a bit.
It took a lot more to fit them to this frame.
1)Remove the screw adj from the rear dropouts
2)Grind a lot of metal off-about 5mm- 0.200" the the dropout so the tire will go rearward more.
3)Shave off the side lugs-then smooth them with sander.
4)It would now fit-at 35psi-with maybe 1mm clearance on both sides-wheels had to be perfectly true.
5)massaged the "dented" part of the chain stays about .020" .5mm on both side with a small maul-concrete block-steel barbell bar.It sounds worse that it was.I had to prop the barbell in place so it was touching the chainstay just where I wanted to dent it.I then hit it with the maul in a rat tat tat sort of way working it back and forth.
The fork didn't have enough top clearance-I will put a spacer in the dropout.
The brake bridge has maybe 2-3mm more clearance.The french frame had lots of clearance-it must have been designed to take long reach centerpull brakes.
If a 29" tire is actually 29" and over 2" wide it would be very difficult to fit it on a road frame.A vintage road frame-one that took long reach brakes-would be your best bet-but I don't know that you will find one that will actually fit a 29' tall 2" wide tire.
I checked my MTBs-the Y50 has about 1" more clearance with a 2.1 Nanoraptor(about 26" tall and 2' wide) so it could fit a 28" tall tire.Same story on NRS-28" max.
Your best bet might be to put a 26" rim on your road frame and use long reach brakes-90+mm reach.
I might do just this on this bike.The mods I did don't make it safer,and they might drop me in the street.
I think it would be a rare road frame that would take a 29" tall tire.There are a fair number of much shorter semi knobby tires that will ork-35-38mm range.Luck,Charlie