I am trying not to change too much - rigid vang would be nice but I need to sail more before I figure what I want from the
rig. I might replace the entire boom at some point anyway.
Original blocks are a bad guide in my case - one is well over 35 y/o - who knows how strong it is. Another is a Schaefer, looks like series 5. I like them, they look very shiplike, and feel solid - but their specs are marginal, 1800lbs SWL.
I just ordered a pre-made Garhauer vang set - it includes both blocks and a
line, so its at least $100 less than me buying those things separately. Plus, their blocks have SWL of 2800lbs which sounds about right. They are "modern style" which to me means - ugly, and won't look right on my boat, but I guess I'd rather select function over form.
I found a sort of a guide somwhere on the net, that suggests assuming for wind of up to 20kts about 1.5lbs per sq. ft. of mainsail for fittings on the end of the boom, and 3lbs per sq. ft. for mid-boom fittings. Continuing this further a fitting 1/4 way from the mast, like a vang, would experience double the load at 6lbs / sq. ft. of main. My main is about 230-240 sq.ft. which makes the load in a ballpark of 1400-1500lbs. It goes up as a square of wind force (but then again, I'd be reefing by 20 kts, reducing the sail size). So, Schaefer is marginal and Garhauer is more than enough.
Other manufacturers (Harken,
Lewmar) have blocks that look even more "modern" (can't look at those things without squinting) and more expensive.
So that's my research for the day.