Dirk-
My original mast and my "uni special" mast both came with these arms. I also came to the conclusion I needed more rake and had the same thought as you (great minds think alike! ). I took the spreader arms off the mast and ground down the rear of the arms to see how much this would increase the rake (I was trying to get in the 45-50mm rake at the time) but it was nominal. Next I decided I had to move the top of the arms away from the front of the mast, pivoting on the rear portion, to increase the rake. I found that by making a small aluminum plate I was able to do this- I had to extend the front of the arms ~1 inch away from their original holes (another objective I had was to NOT put any more holes in this area of the mast ). At this point I learned that several "A" cat sailors had lost their masts due to a small crack developing in the SS pieces that mount the Proctor spreader arms to the mast. Looking at my "contraption" again and considering the cost and time lost sailing if my mast failed I decided the Proctor arms were sort of cheap "security" for a failed mast so I put Proctors on both masts BUT I did NOT use the AHPC supplied front fitting (the one that was failing on some "A"'s) but modified another, thicker front spreader fitting commonly used on some of the monohulls (Y flyers) here. The further you rake the spreaders back the greater the forces they are subjected to IMO and the more important it is they be structurally sound.

Kirt Simmons
T 4.9 159, Flyer 185