Mark -
We build some 15 Experimental Loaders of various design and materials before settling on the design we're now running. The basics of what we've come up with are:
1) All the Steel we use is 3/16 ths inch Cold Roll Steel except for the Mounting Plate which is 1/4 inch.
2) All welds are TIG Welds using ChromeMoly Rod and are Continuous, Top & Bottom and Both Sides, along their total length.
3) All Loaders have a 1 1/2 inch horizontal support of the verticals on top, about midway their length and a 1 inch horizontal support maybe a 1/4 inch up from their bottoms, at their rear.
4) All Leading & Trailing Edges of Both Horizontal & Vertical Pieces are Sharpened Razor Sharp.
5) Horizontal Loading Blades are 2 inches wide and vary in length from say something like 6 1/2 inches to a maximim of 10 1/2 inches so that they unload in the area of the front of the inducer. The seperation between the verticals of the loaders is 2 inches (I.D.).
6) I Speed Coat our Loaders Every Run to Both Help Prevent Corrosion and so that I can 'Read' the Loader for efficiency of water flow ... Water Flow either Shines or Takes Away the Speed Coat.
Realize we're running in a 1/4 mile Race Environment Only so we can Check (And DO) Before & After Every Run. In Recreational Boating, I feel it is Prudent to Check the Loader Every Time The Boat Boat Goes Into And Comes Out Of The Water (Checking all the welds for Cracks) ... This Includes Checking To Make Sure The Loader Bolts Are Tight (I'm Sure You Do This). When a boat goes into storage, I take the loader out and keep it on the shelf until next time.
Looking at the pictures you posted I'd say: a) That's an Awfully Long Loader (Your absolutely right ... Having the tail of the loader right in front of the impeller is Not A Good Thing ... Also, remember Heavier Boats Need Less Dropped Keel & Faster Boats Don't Need Extremely Long Loaders ... The faster the boat, the shorter the loader you can get away with ... to a point) and, b) Having only one brace in the back is Risky ... Might consider what I suggest above as far as horizontal bracing, both on top & bottom. As far as drilling more holes in the suction piece ... I 'Ain't' For That ... As properly built loader doesn't need that in order to function properly and survive.
One last thought ... While your Peak WOT RPMs are considerably less than what we run @ WOT, your running for a much longer time and probably somewhat rougher water ... something to think about when considering my above.
Hope the above helps ... If you need more specifics let me know.
Jak