I bought Marvin's plans around Nov. - Dec. of 1999. After a some study it dawned on me that Marvin and Oscar are both a lot smaller in physical stature than I am. Being 6' 1" and 220 pounds. Great airplane, but too big of a butt to fit into it.
I next realized that Marvin's aircraft didn't have a lot of seat height. OK for the younger crowd, but after 15 years of Army PT, (bad knees) and falling down or having things fall on me, (bad back) I realized that I needed a larger airframe, higher seat, bigger door and maybe a wheel chair.
Marvin's construction is based upon jig building the airframe on a nice flat surface. Since I only have a 100 year old boat shop with a broken up concrete floor, I realized that I needed to be able to assemble the wood structure without a jig.
I sat down at the computer and started making changes to Marvin's plans. I took Marvin's basic airframe and stretched it about 25%. Widened the cabin from 24" to 30".
I replaced Marvin's cabin construction with a series of plywood formers notched to accept the 3/4" stringers. The cabin floor is made from three 1/4" thick plywood formers, two 3/4"x 2"x 6' side rails, 4 corner blocks and some stringers.
One day I hauled this material into my wife's studio and pushed her stuff to the side. It was still below zero in my shop.
I laid the pieces out on the floor, grabbed a 3/8" drill with a screw driving head, a framing square, some glue and went for it.
I spent about thirty minutes test fitting the pieces together and making small adjustments with a hand file.
I glued the corner blocks into place on the plywood formers and screwed them down. Then I set the front and back plywood formers in place, squared them to the side rails and glued and screwed them in place.
Then I set the stringers into the notches and glued them and secured them with some small angle brackets from the hardware store. Next I inserted the middle plywood former and secured it with glue and brackets.