You should make sure the 'track' chainring you have isn't 1/8" thick. If it is, the teeth may be too wide for a standard road chain. If it is 3/32" wide, you should be fine with just adding a big ring. There are exceptions of course; older 3/32" chainrings may still be too wide for modern 10 speed chains. Since you say its a conversion, I am assuming it's not a modern 10speed (10 cogs in back) drivetrain.
Besides that, if it is a true track ring that you have, the countersinking may be on the wrong side of the ring. You may want to flip the small ring around so the countersinking is facing the frame rather than facing the crank. Even if you don't, you probably won't run into any trouble.
Last issue that may arise: If you got new shorter chainring bolts when you went to a single ring up front, you may need to either use the old, longer bolts if you still have them, or buy some proper length bolts for a double rather than single ring setup.