The existing backstay adjuster works fine, but you do want double ended controls led somewhere near the traveler. It's rare to see a race boat with the original fiddle block and cleat on the transom but we did a couple early NA's that way.
These days up to 10 knots we sail with the backstay slack, loose enough for the main to gybe with just a flick on the backstay if the top batten catches. The original spec is 38'2" for the upper backstay, so measure before you cut. The only boat I've ever done this to was hull #1, Warwhoop, which we used as a loaner in the 1988 Midwinters. Remove the upper backstay from the mast crane, cut and swage a new eye at the top—it's probably cheaper replacing the fork at the bottom.
From 10-15 take the slack out so the rig doesn't bounce in the chop. At 15+, when dropping the traveler isn't enough, progressively tighten the backstay to open the leach and depower the main. If we expect to see 15+ all day, we tighten the turnbuckles to take out the slack. The adjuster is more powerful near the top of triangle. I've not convinced the backstay does much to tighten the forestay upwind, but downwind in a blow (25-40) a bit of backstay helps keep jib luff from bouncing around. And the rig onboard.
