Is that the Eric Collins grill cloth? Sure looks better than the regular stuff & I like the black covering! I did put the Eric(EC) Collings cloth on my combo along with a metal, early JTM45 coffin logo plate.
The GZ37 & the 5U4GB are the same valve so don't buy one of those thinking you can get away with using it I like the way they drop the voltage down, but you can ruin the mains tranny on the amp.
Is the Mains tranny for the 50th Anni. amps the same and are they able to be wired at 240v & 120v using the same tranny? Some Marshall's use the same Mains but the wiring is just configured different.