Ah... you're getting off the track there, Don!
The 300SLR was a straight eight, this discussion is about sixes, and I have a reason for that.
How about I throw one in to keep the topic going?
The Repco-Holden engine, the darling of the midget racer set here in Australia from the late fifties through the early seventies.
Based on the Holden 'sideplate' six that came out in 1948, it was rather like a scaled down Chevy, 4 mains, originally 3 1/8" stroke, 3" bore and capable of delivering an effortless 75bhp. Standard, that is, before Repco started work on them
The 'Repco' part of the equation was an aftermarket head cast in iron but formed with care... looked great with a rocker cover similar to the early 'Spitfire' Poly Dodge engines, but most of all it sounded fantastic!
Repco bought a Raymond Mays Zephyr head to study as they went into this project, but I suspect that more of their input came from the Maybach engines they were constantly upgrading for Stan Jones (Alan's father) in his quest to win the Australian Grand Prix and from things like the Chrysler Hemi and Peugeot 203/403, as these all had similar valvegear.
At full cry in a midget hustling round the 1/4 and 1/3-mile ovals, it really sang... a howl you never forget, the howl that has endeared me to inline sixes forever.
They were also used in boats and road race cars, principally to replace Bristol engines in the Cooper-Bristols that struck trouble here. The got bored out to 3 3/16" or 3 1/4"...
In short, a great little performer built out of a solid but mundane basis. Whether it was in fact based on some discarded plan for a small Buick or Cadillac (I doubt that...), it became the staple base engine for Australia for a decade and a half, Repco's contribution turned it into an inspiration.
