29er is a mtb term for 700c.
There are no vintage "29ers"
Especially if you want front suspension.
You could go with an old cyclocross or touring bike with cantilevers. Some touring bikes will have had "27" " wheels originally, getting 700c to work with a cantilever braked frame that had 27" is problematic or a no go.
If you wanted front suspension... A chore too as the majority of steel frames had 1" steerers.

Most guys bought a cyclocross bike 2cm smaller than their road mount, so top tubes will be longer with the smaller frames.