Edcor does make a suitable transformer, the CXPP25-MS-8K/23%. I have a pair that I had ordered for a ST-35 because it has a 16 Ohm output for my JBL 2420 16 Ohm compression drivers. The problem is that they are somewhat larger than the Z565. I tried them on a standard ST-35 chassis and thought the layout was much too crammed together. I could have made it work,however.
I, instead, purchased a pair of Z565's from Triode. (And a Diytube chassis and board for the Edcors, not yet finished.) The Z-565 transformered ST-35 has been running for about 2 months and sounds amazing. Much better than any of my SS power amps, of which I have a few.
The only real change that I made, from stock, was a set of Mundorf silver-in-Oil coupling capacitors which had to be mounted under the standard ST-35 chassis. (They just barely fit). The amp sounded a little bright and somewhat harsh until everything settled in. Never has any single component improved my hi-fi- setup as much.
You've made a good choice in the ST-35 Dynaclone