Probably will do fine.
On my 1980 Cherubini Hunter 36, I've been using for several years now a used full battened mainsail ex a Catalina 36, standard rig. The foot is about 9" shorter than spec for my boat. And the luff is about 12" short (maybe a bit more).
Works fine. I've still got to reef it when the wind gets to the 15 kt range. I've not had tendency for lee helm -- still a safe weather helm with any sort of wind. My Genoa is a 135, so I've got plenty of sail area.
Our boats are mast head rigged, so the head sail is the main motive force for the boat anyway. My boat sails awful with just the main up. Even, with the official spec'd main sail. But does very well with only the head sail.
Since I got the Catalina sail, I did again try my "official" main sail to compare. Can't say that I noticed any real improvement. But it does look a bit more impressive with the head all the way to the top. I didn't keep it on because it's cut allows the boom to drop just below my 6'4" head height when I am in the cockpit. The Catalina sail's cut keeps the boom a few inches above head smack range. When I do eventually buy a new sail spec'd to my boat, I'll insist on a cut that keeps the boom safely high ... even if some performance is sacrificed!
Except in light winds, my guess is you probably won't notice any decrease in performance. Although you might be going a few 1/10's of a knot slower at most.