I’ve never compared the schematics to the 800’s either way the sovteks have voice of their own there are enough jcm 800 vids on youtube to compare your H’s tone. I play thru the B version as i play bass and love it, gain is alot less than your H the schematic for a few migs can be found here http://www.webphix.com/schematic heaven/www.schematicheaven.com/post70s.html
I have the schematics for the B, and standard 100 both having less gain than yours i’ve never seen a U schematic i’m not sure how it differs from the others.

As far as the Green bulb goes you’ll need to size up the hole and find a bulb that will fit they are powered off the 6.3V heater supply. Speaking of which the first 2 tubes are heated by 12V DC and the PI and power tubes are 6.3V AC grounded thru the cathode. I’m using 6ca7 power tubes(mods needed) in mine and love them alot more than the 6l6’s the sound seems so much fuller i think maybe they arn’t as mid scooped as the 6l6’s.