I think the 20 sized lay downs were better than the upright but I am just guessing. We won US#1 twice with the 20 size.
The K&B engines with the carb on the side were perfect in a lay down configuration as it made the carb upright. We did have some trouble with the carb on the side if you got ANY water in the engine compartment. That is what started me thinking about doing it.
I remember going to Ft Worth to the Internats and we took 4 laydown 21's. For Myself, Howie Whitaker, Don Bilsky and Mike Wisniewski. Mike was th Son of the K&B engine designer Bill Wisniewski. Mike brought all the engines for all 4 of us. The boats were really strong in heat race trim and competitive in SAW and Oval trim. I remember that Andy Brown and a couple of Norwegians were also super strong too in the 21 class.
The 67 size is a different story. It REALLY looked cool but was difficult to keep the engine tight on the mount. If we would have been going as fast as we are today, it might have been a little better.... Who knows.
Probably more than you wanted to know, but I couldn't skip some Nostalgia.