If not a Busso, it would have to be a 308/328. Authentic transmission, cheaper and more power than a Dino.
That doesn't really fit the 'something plentiful' bill though, does it? You really can pick up Mondials for £7k to £10k though.

There must be a transverse gearbox you can use with the Duratec/Jag V6? Didn't a Noble use one in that configuration, and the new mid engine Ginetta too?