I would start with the rating for the SX.
Then, check the sail area of the Tiger main versus the SX main. If it's the same area, take the hit for it being a square top. If the Tiger main is smaller, it may be a wash.
Leave the wings at home for racing. There used to be a Hobie-18 formula rating, which I believe was essentially a SX without wings. Could be wrong on that. If there is, you can use that as the base rating for no wings. But - if you use the regular Hobie-18 rating, know that there is NO hit for using or not using the wings. In other words the rating for a Hobie-18 and Hobie-18 magnum is the same.
Take the 0.995 hit for non-standard spin against the SX rating.
Rudders and boards - the stock Hobie racing rudders have carbon fiber in them. I'd use them and avoid the hit, they're nice and stiff. As for the boards - if you're going to take a hit for different (carbon) boards, there's something I always wanted to try - making inserts to fill the stock trunks a bit so that you could use a modern high-aspect foil. I always thought another stock Hobie board would work well, say a Tiger or Hobie-20 board, maybe cut down a bit if you find you don't need the length. IF the inserts are done right, they could be removable to return the boat to stock. If you're going to take a hit for non-stock board, go for a non-stock board...
If you start with the SX rating, there shouldn't be any hit for shroud lengths or whatever. Which brings me to my next point:
In most cases a race committee is not going to sweat down to small details for the non-stock rating hits. If you have a non-stock tramp, non-stock blocks, etc., they shouldn't care unless they're anal. They should worry about the big stuff - spin, main, jib, major alterations and refits. If anybody sweats a higher purchase downhaul on a modified '82 H-18 they'r missing the point IMO.
But - when you do show up to race, show up with a sheet detailing the mods you will claim, and calculate out the numbers for the committee to help them along. And don't just do DPN, do all the wind corrected numbers as well.
My $0.02
