RE: use of weed fins on evo and acid
While I'm sure there is some "effect" on the feel of the board with a weed fin, I think for smaller boards, like the Evo, there are some "options".
Other than the OEM Drake fins, many wave and surf type fins already have significant ramps to them, and with the quite curvy and swept back planforms, I'm not sure that the COR (Center Of Resistance) is
moved as far back as you suggest.
Many wave and B&J fins have alot of their chord in the "swept back" lower portion of the fin, and these fins are thinned out and have significant bend or twist similar to the "flexy foil" surfboard fins.
Wolfgang's Duo fins shed weeds (eel grass and similar "leafy or round stock small diameter weeds) by a different principle than simply using the Leading Edge (LE) angle. Since Wolfgang's fins are "assymetrical" the weeds "flutter off" the concave side of the fin.
You might be able to get away with a much steeper LE angle and use the assymetry to shed your weeds.
This won't work with larger diameter "weeds" like kelp stalks, but as with all "weed fins" you need to match the fin style (and it's operating principles) to the types of weeds you are actually encountering.
A number of fin producers make "surf weed" designs, and it's pretty easy to put the screw at the back of the fin vs in the front for this type of fin.
Biggest problem with the Evo's is the very short fin box, that does not allow much additional chord length (at the base of the fin) beyond the OEM supplied fin.
Since you are making your own fins, you could easily extend the ramp
beyond the front of the fin box (this will require some close tolerancing between the overhang and the pin, but it can be done and you would getdecent gasket compression on the overhang gasket, or you could "fill and fit" to your particular board). 3 cm (1.18") is not too much of an "overhang" to deal with.
I'm not familiar with what sort of weeds you get at San Carlos, but if they aren't of the thin flat "eel grass" variety, you may get away without a ramp and perhaps with a bit steeper LE angle.
Yes, it will effect the "feel" of an Evo, but in many cases the use of a weed fin with a significantly longer chord and alot more "chordal twist" (like the flexy foil surfboard fins) it may make your board feel better and stick better in your bottom turns. So, the "change" in the feel could be a positive rather than a negtative.
Hope this helps,