Not production, but the 400ci SBC that was in a few cars, the 350Z was one and Max Wilson's Contessa Gold GTS350 another. The 350Z was never registered but the Gold car was.
Also the BBC (427 I think) and the LT1 350's tried in HG's.
As for production engines my guess would be a low compression engine, maybe the low comp 308 in Bedford trucks and buses. Or maybe one of the later engines in low comp like a WM in a WB or a VM (red or blue) in VB-VH. Might only be sold in the 100's but maybe not as low as the 150 x final spec XU-1 engines.
I'd also think if we were going by engine number rather than actual engine something like an XQE or XZE (auto low compression ADR27A LX or UC) would be very rare, but they are the same engine as a Holden QE or ZE with the X stamped in front for Torana.
WT would be very rare as well (WB commercial 308), only a handful of these would have been made without the 11 or 12 Statesman prefix..
Edited by yel327, 22 September 2013 - 07:34 PM.