Well after a lot of head scratching

and template cutting I think I have found the best fit for a holding tank beneath my V-berth on my 1966 Overnighter.
Thanks to you guys I got clued into Ronco Plastics, yes the same company that made the vegi-matic, and am ordering a B431 (35 gallon) holding tank. It is as close to a perfect fit as I can hope for. It fits between the first and second latitudnial v-berth support (from the bow aft) and is angled almost exactly right to match the outward slope of the hull. And being only 16" long but 54" wide I can still reach the forward drain plug with a little twisting. I can't count the hours of measuring and fitting I went through before feeling safe about gambling $500 on a chunk of plactic. There are hundreds of holdink specs at
http://www.ronco-plastics.net/ with very few being plain cubes.
Thanks All
"
LIFE is what happens to you, while your making other plans."