Just in case anyone is interested I had an email back from Guy.
He was incredibly helpful. He pointed out the issues with changing things but did suggest a change of some coupling caps to help with low frequency extension.
He suggested some NOS valves to try too but also said don't spend too much.
It had gone in to be checked over with someone locally so I asked if he could carry out the changes that Guy suggested.
He did the changes and I picked it up yesterday. He even gave me a Mullard to try.
Had a listen last night and first impressions were that the bottom end was slightly better. May have been confirmation bias who knows.
On to tonight and I couldn't wait to try the Mullard. Changed it over and I've been listening to the same albums as last night.
First impressions are very good. It's just better.
Spot the difference