OK Just got back from the lake, but the wife left the camera there. Sorry. I did measure my bunks and I think (they were hard to measure without getting in the water) they are 42" on the outside and I thought they were 2" wide beams, but I can't remember so I may do it again. Actually looking at the pics, the actual bunk itself is probably 3" wide.
Ah wait I found some pics:
Notice how the bunks should be at the rib closest to center? If they are a little too tight, your boat may sit lopsided as mine did before the offset brackets were installed on my Sunstream lift: Either way just measure the ribs closest to center and your lift bunks should be closer together or just further apart, like mine is.