No doubt ill have a thousand silly questions for you Steve,, but first off, what engine and box are you running? And who built your engine and to what spec?
Si, as I said before, I'm not a slave to originality, so the engine is from a very rusty early 70's Trans Am I used to own ...... yes, it's a Pontiac

So, the engine is a early 70's Pontiac 400 (6.6 litre) with a Richmond Super T10 4 speed (as originally fitted to the Pontiac and similar to a Toploader).
The engine was rebuilt by some bloke called Steve Brown (machining / crank regrind by
http://www.realsteel.co.uk/ in Uxbridge. The engine has Edelbrock Performer Plus camshaft & intake manifold, Holley Street Avenger carb, custom headers / ignition. Apart from a light honing, bore / stroke are pretty well stock. Pontiac engines are renowned for being torque monsters and don't need to rev to silly numbers.
In a car this light you don't need silly horsepower to put a big grin on your face. If you're going the 289 route, it really needs to be small block Ford / Toploader (although I've known people to fit the T5 (Worldclass spec) to a Ford 302). Modern gearbox alternatives are Tremec TKO500 / 600 - a five speed - which would be well suited to a 289.
Have a look at
http://www.roadcraftuk.co.uk/ for bespoke engine / trans packages - they are very well regarded in the kit car / US engine worlds.
If you are looking at building a 289, the UK marketplace is pretty much only
http://www.hawkcars.co.uk/ There are also some good second hand Hawk 289s about - builders tend to go for originality and hence would suit your idea of 'the gentlemans sportscar'.