Im pretty simple myself compared to many of these gents. So, from a simple guy to a simple guy, as already suggested, replace the output caps with films and do the Speedball upgrade. I would do them seperately as suggested so that you can hear the effect of each one.
Speedball makes the largest difference. Output caps probably the second largest. The other stuff generally requires a lot of real estate with several largish - large replacement components to make what very well may end up arguably being less of a difference than either of the other two relatively easy/simple upgrades mentioned. In other words, more of a cumulative effect from several mods, not just as single mod like the film caps or speedball. Check the Gallery forum to see how far some builders have gone.
For those output caps, Solen 100uf, Axon 90uf, Mundorf MKP 100uf, Erse 100uF and Dayton (Parts Express) 100uf are among the affordable and readily available film cap options.