1/2" is pushin it for a wax seal. if the toilet clogs below the flange, you could have a pretty shitty blowout (pun intended)
1/4" is the most i`d float a flange. The wax seal isnt made to handle much more..
Get a flange extender, shim and screw it to the subfloor.. Then you can use a regular wax ring, without the funnel. I dont prefer the funnel, have had some clog issues with them
extension kit--> »www.amazon.com/Oatey-43645-Close ··· extender
If you do decided to try using the old flange, make sure to get a new set of 5/16" closet bolts.
if it aint broke, tweak it!!
currently on FiOS (kick aZZ!)