One of the smaller issues I have is as V4a will be the tremolo oscillator and as this build will not have a reverb circuit thus at the moment V4b has nil purpose or job to do. Normally in a VOX AC series amp V4b would be the reverb recovery amp and a V5 tube the reverb drive amp. So what to do with the spare V4b?

Anyone have any useful suggestions?

As a side line, in my searching I have uncovered a number of useful and informative web pages.
https://robrobinette.com/How_the_Mar...M800_Works.htm is a bit technical however gives excellent explanations of why thing are as they are in Marshall designs and helps with understanding other tube amp circuit designs, and to some substantial extent about tube amps in general.