I have already ordered your ST35 pcb.
I would love to hear your thoughts on using the AI S300 output transfromers with either 47 or 100R from a - g2. The standing current could have to be reduced by raising Rk ..... Then comes the playing by ear. They are 9K('ish-not too sure?!):8R. The ST35 calls for 8K:8R. My seEL34 sounds better on the 8R taps than the 4R ones, even with KEF 103/3 (4R). The output available would only be (max)10W, due to transfo, but would it work?
Next question is the mains tranfso from the AI s300. Can I run the EL84 from this? Ia maybe down to 30mA? (your board looks nicely adjustable!).
re Mains transformer: I can find no ratings for the transformer, but it did feed 4xECL86 and 3xECC8*, so should just about manage the heaters. As for the HT, I have little hope, showing only +285VDC at CT of O/P transformer in most schematics. Maybe keep the o/p's and find a new mains?