Sb/bb?

Here are some links that I'm considering on the SB issue of things:
318: http://www.speedomotive.com/ps-138-13-mopar-318cid-to-390cid-forged-piston-stroker-kit.aspx

340: http://www.speedomotive.com/ps-139-13-mopar-340cid-to-392cid-stroker-kit.aspx

360: http://www.speedomotive.com/p-140-mopar-360cid-to-408cid-stroker-kit.aspx#KitInPostBack

The three kit's look to be the same kit, but tailored to the blocks spec's... IE different bore sizes... And what ever else. For the BB's, why put in a stroker kit in such a light car?