I'm not sure how much you could offset the hangers. It might work. Probably easiest to play around with the uninstalled seat and see how it hangs when offset.

The one problem I encountered installing the backband on a 17lt was that even a very small cordless drill was too long to fit between the bilge panels and the under-deck to drill up into the coaming from underneath. I needed to get a right angle drill to be able to drill those holes. Possibly a flexible shaft or some small dremel type tool might work. If you place the bulkhead too close to the coaming edge, consider how difficult it may be to drill holes for those screws without punching out through the back of the coaming. (What happens if your hole is not drilling straight up into the coaming. Don't ask me how I learned this!:)

Screw it into the coaming.  I would think to support it directly above the straps for the least stress.  I hope you don't want to move the bulkhead forward.  I would not want to lessen the cockpit space behind the seat.  I use that space for drinks.  On my 18 I tossed aside my RP backrest and put in foam.  Actually took the foam pad off the roof of my car and it made a great back support. 

 Kim

Agree with Mr Kim, I put my camelback water pouch back there and run the drinking tube up into the cockpit. Convenient for me....

I find the rapid pulse fine though and haven't felt any need to do something different.