Dave doesn't have T-tops, just the targa roof. I don't think he will offer one, either, due to the complexity of making the actual T inserts, even though he has an open offer of mine to use as a pattern.
Here's the dune buggy support:
My first car in it's raw state. Yeah, it was a "T" top *humpf*... center spine was as wide as the handle opening:
And later in it's life with a metal ring support all the way around the opening:
And the Rose car with a factory T:
So.... it's not so much about cutting the roof, but making it watertight again with the inserts. Probably one of the neatest solutions I saw was in a newsletter 'back in the day' where one owner took a set of his and hers sunroofs from a van and installed those. Those used to be really common... sometimes they come up on eBay from time to time.