Any info/history on #003?

[David]

... Ideally I'd like a trophy blue v8 with a super charger ...

There are two supercharged 260s known to exist in that colour, but I think both are "spoken for". There are several in Ignition Blue and a couple in Chagall, but none are known to be for sale at the mo. There is however a Royal Blue supercharged ZT-T for sale currently. Check out post #18 in the Complete List here: https://www.two-sixties.co.uk/mgoc26...-260s-FOR-SALE

... Dumb question, but when do the belts need changing on these v8s? And is it expensive?

260's don't have cambelts, but chains which last at least 150k miles.
Clutches can be expensive, being an engine out job really. A noisy diff can point to an expensive problem (£1k-ish). Rear subframe and front struts, rot in both cases, are also known to be (commonly needed) expensive items.

David