I realized this afternoon that I hadn't commented back on the final outcome with my fuel tank replacement.  Good new!  After I mocked up the new tank, Bud was kind enough to have the tank built and the install was a piece of cake.  I included a couple of pictures below in case anyone else has the same task and is looking for a reliable way to mock up the tank.

My first mock up was in cardboard but I was concerned it might be flexing in ways that the final tank would not flex, so I transferred the card board cutouts onto 1/4" plywood and used drywall corner and screws to build a more ridged mock up - it worked perfectly.

I hope no one else has to mess around with it as much as I did but, where there's a will there's a way.  This smaller tank holds 30 gallons, a reasonable amount for my purposes. 

Don 

Sorry, no dimensional drawings.  I used Bud's standard starboard fuel tank, took 2" off the top width and reduced the length by 6" from the aft end of the tank, the bottom stayed the same dimension and all other dimensions shrunk accordingly.  Don