Upgrading the W5LET Transmitter

[N0WVA]

Looking for a mod.transformer to upgrade my s-g mod. transmitter. Its the one out of the Sept. 67 Electronics Illustrated by Jim White W5LET. It used two 807's in paralell. What impedance do I need and can I buy one new? Ive been hoarding NIB 807's to build a modulator....I have 6 extra tubes, so I plan on being around for awhile! I used this rig as my main AM TX in the 90's. its been in storage and I need to upgrade from piss weak to average.

I read the article on power transformers, but , but Id really like to do it with the correct impedance/ratio.

Thanx,

Doug