Well, I played my Tremolux with a EH Holy grail for quiet a while. It was pretty close to the on board reverb of a twin imo. (Played a SF Twin one one or two occasions, so I can't really tell) but a previously used a SF Bandmaster reverb and the EH Holy Grail with the tremolux actually sounded nice then the Bandmasters reverb. Just make sure to keep^the treble on the amp below 7 or so and ad a tad more bass. Both normal and tremolo channels sounds nice with the EH Grail. I like the tremolo channel most with the no. 1 input and bright switch on, but depending on the speakers you use you van leave the bright switch off. I used the tremolux with 4x12 Celestion GT 75 for a long while before sizing down to a 2x12" Jensen cab.
Always liked the Celestions. GT75, Vintage 30 and the greenbacks.
Despite owning a "66 BF "blond-ed" Single Showman, I prefer the Tremolux. These things got some magik imo.
Just started to use my old Eko700 turned down to B on it and its instant 50ties baritone sound....

I only used the Showman when I really needed tons of clean and a lot of volume (read non PA-ed gigs in open air)
Now the Showman collects dust, which is a shame actually.