Is it possible to adapt kt88 to a 6A3 single ended

I have no clue but almost anything is "possible".

That doesn't mean its a good idea to do it though.

It generally does not pay in the end "to fit a square peg in a round hole" as they say unless there is no other choice. Especially if the consequences are uncertain.

Charles,All wild guesses and even ask him if he does

You didn't answer my question. Any how, if you do proceed with this amplifier project, let us know your result.
Charles,

Wow! Note to self. Watch for a gently used 6A3 amp to come up for sale soon.

Real,

There is a difference between "wild" and educated guesses.

Knowing Al and his background and interests and having read many of his posts, I can assure you his guesses are among the best educated you will find.

Since you asked the question, I'll assume you do not know the answer for certain either.

So there you go.

If you find out anything better or more definitive, please share here.

Whatever you do or not, be safe in doing it.

Thanks.