I have to admit I'm not a fan of our host's trials tank either, too slim and not round enough. For some reason the version they offer for the EFI trials (93580) is a better looking piece of kit, though whether it would look as good with the funny petrol tap adapter plate is another matter.
The best alloy tanks I have seen for the Bullets were sold by Watsonian Squire in their time as the RE Importers. One was an alloy copy of the basic roadster tank, which they referred to unofficially as the Tadpole tank, the other was a copy the Greeves Scottish design adapted to fit the Bullet frame. Both had Monza filler caps, though heaven only knows where you'd find one now, as they sold out of these long before our hosts bought out their spares stash. Keep scouring ebay, Real Classic small ads and your nearby autojumbles, also anyone who has been a RE dealer for the last 15 years at least!
While you weren't asking about steel tanks, the small chrome panelled tank looks nice with the late 50's badges, particularly so with a thick and a thin gold pinstripe around the embossed section where the chrome panel sits.
http://www.hitchcocksmotorcycles.com/ht ... e92674.jpg
The late Interceptor tanks are a pain version of these, but chromed:
http://www.hitchcocksmotorcycles.com/ht ... 49555C.jpg
A.