As for the V8 being set at a 90 degree angle, that's because a 4 stroke 8 fires every 90 degrees, so the block has to be 90 for the simplest crankshaft configuration.
The 90 degree (270) Triumph twins originally produced the same power with a bit milder valve timing as the 360 engine. The whole thing now is that the 90 degree engines are seriously detuned for emissions control. They are probably able to tune the Thruxton engine properly because it is a low prouction model.
