Years ago,just to see if it could be done,and there might have been adult beverages involved,I stuffed about a22- 24 pounder in.
I don't have records with me.
Seems like I trimmed the tail,some wing tips,etc and forged ahead,where others have the good judgement not to tread.
I had used a brine similar to Smokin's and did use TQ-just in case.
It came out acceptable.
My choice,if I want that much meat is to cook a couple of 12-14 pounders.
I cook the first one a day ahead,do all my carving,and ziploc in the refrig,over night.
I do the other on serving day.
I reheat the first one,which I think is better that way,and present it around the whole one,on a large platter.
I also cook 12-14 lbs,even
if I am cooking hot in convection ovens.
Besides younger,and I think more tender,they just cook better for me.
I also like to do as dls suggests.
I cut out the breast,from the leg quarters,use the back and wing tips for stock.
Cook the leg quarters early,and add the whole breast later.
They can come out together,that way.
You can do two birds,all dark and then all white.
Practical is good-on busy days.