I would redo it with axial caps. and copy the grounding scheme of the caps in the schematic. Like with these https://mou.sr/3RzbZWl and redo all of the 30uF with the 33uF @450V. Mainly they look good to use and their axial. I would get rid of the extra cap too.
Just looking at this photo, there are a large number of points that vary between the left and right output, it might be worth putting it all in order.
Ok guys, so an update - and thank you for the input. Turns out in the post above in the photo, the 10W resistor had a jumper underneath on the terminal grounding it. Once I removed the jumper, hum got considerably better. The other ground for the bus is over by the filter caps (long white wire running from a terminal strip to side of chassis). I am now trying to figure out how much more hum I get with both grounds lifted - I have a feeling I am going to need a ground from the bus at some point. The hum is still present, but it's presentable - it's almost like it is the subtle hum you would expect from a tube amp. I don't know how much better I can get it. I think I may move on to voltages and see if I can live with the little bit of feedback I am getting from this amp...
That's good detective work there, nice one.
If you can get noise & hum below a few mV you'll have it sorted. To do this on an existing amp can take a bit of time. If you connect it up to a dummy load and a scope/DMM, then try lifting grounds & use a small metal plate grounded through a jump lead to shield any magnetic components from high Z inputs whilst keeping an eye on the scope/DMM should give you an idea of whats what.
Sounds like your heading in the right direction, well done.
Andy