Andy, I did exactly those two retrofits on my boat. Check out the last two pictures on page 3 of my website.
http://groups.msn.com/RogerConrad/shoebox.msnw?Page=3
I used the inspection port insert to locate and draw the outline of the hole with a fine tipped felt marker, then a dremmel tool to punch holes along the line, and the 'join the dots' to cut out the circle. I next used marine goop to seal the rim to the hole, drilled and bolted the rim with ss bolts, and that was it. There is no solid foam behind the seats, so be prepared to fetch the 'hole' when it falls inside.
Forward of the bulkhead is foam, so if you need to get through to the back of the boweye (about 18 inches forward), you will need to dig a tunnel. But that is another chapter. I have pictures but not on the website. If you need to see them, let me know and I will e-mail them to you.