The two chain setup to the tractor drawbar does two things... limits the downward movement of the main mower frame, and, when the three point is lifted, makes the cutter bar lift in relation to the mower frame, first the outer end, then the inner shoe end.
The operator's manual (at least the one I) have explains the downward setting and gives some tips and chain link counts for the lift chain and and lift assist spring and chain to make the mower behave as it's supposed to. With my mower, it took a little tweaking and wrestling with the BIG ornery spring to get it to all work in sync.
There are two basic frame designs, which affect how the narrow or wide configuration setup gets changed. Mine is the older design... swap the drag bar pivot pin to the other hole, then tip over the lift mechanism and re-attach the chains to the holes at the opposite edge of the lift bar.
Here's a photo from a couple of years ago, showing the older-type 350 I have.