Well Smitty, your latest good words about the changing period into the outboard full open racing classes is quite interesting but mostly after my time with Jim Hallum. Jim and I had spent much conversation, and some detailed thoughts, about fitting the better mid-1960's motorcycle engines to outboard racing use. You have provided a nice overview of the later conversion successes and Jim sent a set of DVD's he made that showed the more current small racing classes using current motors & maybe some of the earlier conversions. I think that DVD set ought to be kept in an SOA library rather that go extinct with me out here in the hinterlands.

But more of interest for early moto engine to outboard conversion. It was about 1965-67 when we were out at the farm shop and thinking about some practical way to adapt the current 125 cc rotary valve Yamaha single to outboard racing use. The issue of engine approval was a question but since the motor was certainly a production engine by the thousands we thought that use was possible in the NOA if not the APBA. You previously told of the Bill Tenney twin Anzani gearbox to tower housing setup used one final time by Hallum and Anderson. That setup was the basis for a rough design drawing Hallum made which placed four of the 125 cc Yamaha motorcycle motors into a configuration which used the Tenney bevel gear system similar to the coupled Anzani's but with 4 input shafts, one on each face of a cube gearbox. As I mentioned earlier, this 'imagineering' was a fun exercise but Hallum was serious enough to make a fairly accurate rough design drawing. There was not a chance at that time of any actual construction.

The output of four "full modified" 125 cc Yamaha running alcohol was going to be something near or over 4 HP per cubic inch so the "Square 4" 500 cc Yamaha setup was likely to have 120 HP and loads of torque because of the basic bore/stroke ratio which I think was the same as the Factory RD-56 250 cc twin Gran Prix machine. It was also not going to be a light motor hanging on the transom; maybe no worse than two iron B Anzani's though.

Hallum & Dunn's first effort for the road racing 125 rotary valve Yamaha did prove out the horsepower range estimate using gasoline so the 500 cc outboard configuration would have been impressive right from the beginning. Probably would have needed to fit it to Charles Walters runabout for safe enough use though.

So there you have it, another snippet of an early interesting effort by Hallum before he got busy doing the rather outstanding post-Anzani workings.
Fun times later but I missed almost all of it unfortunately.

Another tidbit Smitty. In 1962 at Lake Lawrence, 1 2/3 mile record course, I ran over the record with my 1955 Entrop hull in DOH but by not enough to make the books; worst start I ever made at 3 seconds behind the clock. Finished well over a full turn ahead. Surprising super smooth ride with the transom off of the water except for the last half of each turn. Much lament over that lost 3 seconds since it would have put the DOH 5-mile record in the books until almost 1970. Wasn't wise enough to find $5 to buy the Bob Carver turn entry photo. A month earlier at the Divisionals in Estacada, Oregon I also finished with over a full turn lead but threw the shear pin in heat 2. I think it was Howard Anderson who won on points and got the guarantee to run at the Nationals. Am pretty sure that he won DOH at those Nationals so was was a fast fellow. OK then on your "gear head" description but I was plenty quick in DOH for a few short years. Fun times then too at age 20.
Russ Rotzler