Just to be a tool, you really want the "grunt" at the top.....

You just want to be sure that the valve train geometry and camshaft choice matches the port design of the heads, personally I'm not seeing the Vic Jr.'s being a good choice, but know little about what you are building.
Personally, I am all about big round ports, I don't like to see rectangles unless we are talking over 6K RPM or artificially boosted (turbo, supercharger etc...)
If your motor guy is recommending them, it wont hurt his feelings if you ask why or ask if he has somewhat of a case study on another
JET boat.
I don't like to be told something will or will not work unless somebody can back it up with a reason why. Or at least a theory of how.
GT
edit;
there is a problem that I can't seem to get past... grunt at the bottom
always means oval port, you are saying rectangle, hmmm...
Also, on a centrifugal pump, there is no such thing as "grunt" at the bottom....