UIM OE class racing 1975.
I found this German article from the European championship race in Brodenbach.
WOW..memories are flying..In May we raced the World title in Aix-les-Bain, France and Roger Jenkins won (defended his 1974 title) in his #1 Burgess/Johnson.
(See smaller article)..we both used a very powerful OMC race engine but my Burgess was 4 inch shallow in the tunnel instead of Jenkins 6 inch. Paul Kalb ordered my Burgess this way. Very fast but impossible the race. ( I crashed bad at the OMC in early May and the boat was repaired for Brodenbach.
Rain and strong wind/waves ruin our weekend in Brodenbach.
Both Roger and me broke down. I now see I ended up 10th.
Hans-Georg Krage did a great race and won in is hydro.

Pretty sure this picture below is  of the two OMC real UIM OE/APBA Mod 50 class race engines in Europe 1975.
Jenkins raced one and I the other one. We could only use them at a few races.
This picture is from Cardiff 1975 and its not a production mid section. This mid section used a racing gear-case without shifting.