There are three "thunderbird" versions out there.
The original T Bird kitted originally by Veco was 595 sq in wing area, p 40 style canopy and an upright mounted engine. I think now kitted by Brodaks, The New Thunderbird kitted by Veco and later Dumas. 605 sq in wing area, p-51 style canopy, inverted engine, differential flaps, and over/under leadouts-- I don't know if it is currently being kitted by anyone. Then the Thunderbird II which was not kitted back when it was designed, but is now kitted by RSM and possibly others that I am unaware of.
If you built yours from a Veco or Dumas kit, it had to have been one of the first two I listed.
Good luck.
Bigiron