Hi Bob1307
Scan the bulkheads from the plans and save them as PDF files.
Measure the bulkheads in mm's and to get to 6.5 inches(165mm) calculate the % difference and in the printer setup you can custom print to the required size.
Not allow for the fibreglass thickness.
The fibreglass hulls I use to make only required decking frames and a stringer around the inside between.
One of the customer's ask about the strength, so I weighted to the water line, lifted it to waist height and dropped it into the water!!
Dam nearly sunk but pop back up with no water in the hull and no cracks(no deck frames install at the test).