The bows will handle 29", it's just that the standard for measuring weight is set at 28".
I have numerous old bows that I shoot regularly. This past Sunday I shot 3 or 4 dozen arrows with my '56 Kodiak Special, trying to tune the twang out of it. Later, I picked up a '60 Kodiak Special and shot several dozen with it. I would just be carefull the first time that I pick up an older bow. Check it over looking for slight delaminations or defects. I like to flex them a bit, half draw and shoot, and after a little while just go for it and shoot normally. I haven't had one come unglued yet.