Quite seriously if someone wants high performance and a lighter and rather more simple setup than the Roadster they should talk to Williams about the Duratec 2.5 4 cylinder that Omex built for them. I saw the engine at Omex as it was nearing completion. An impressive piece of work. Photos at
2.5L Duratec VVC 290bhp/240lbft engine build for Williams Morgan I don't know but can imagine that they could also build an engine in a slightly lower state of tune if required.
Sorry about the thread drift