I agree with Top Hatt... go with custom fit if possible. Years ago I did basically the same as he's proposing, keeping the width while extending the length from 8 or 9 inches to about 14 inches. It worked great. I think that by extending the length rather than adding blocks or other ways to increase the down angle is the proper way to do it. By adding angle you get to a point that you have increased drag too much for the gain in lift. A more gentle angle with more surface area doesn't create the same amount of drag. One word of caution however is that although you may achieve what you want in performance, there arises the danger of broaching in a following sea, especially when running an inlet. You need to remember to totally retract the tabs under those circumstances. The same caution is required on long passages at higher speeds because as the fuel is consumed, your trim angle changes as well. It's easy to become complacent (or lazy). Please be careful.
One other word on my experience was that I needed to use 2 cylinders on each tab, but mine were over 12 inches. Check it out with Bennett but I can tell you that they will advise you against 14 in or more as a means of CYA on their part. Any good sheet metal/machine shop can bend you up a set pretty fast, there's not much to it. I used 1/8 in thick 316 SS for mine which was probably a little overkill, but I had some in the scrap bin so I figured, what the heck.
Walt
