To mod that would probably lead to regret. I had a ‘78 for 10 years and towards the end, possibly out of boredom and partly because a band mate had an 800 with the same mod that was amazing, I got Soldano to do his high gain mod to it. Lived in the same city. The minute I played through the amp after it was done I was like…Fuck..I guess I shouldn’t have done that. It couldn’t touch the stock amp with pedals and I no longer could get close to the great stock sound by lowering the gain knob. I sold it soon after. In hindsight I should have had the mod removed but this was back when you could easily get another one for about $800-1000 and like most of us gear whores, after 10 years wanted to try something else. Not all 6 knob Marshall’s react to the same mod the same way, so even if you hear a modded one that blows you away, you may not get the same result with yours.
Plus, your clips with pedals sound friggin’ fantastic. I don’t see a mod beating what you’re getting already.