Pacific Interior Flight Systems in Canada installed split doors like a PA-18 on their "Super 12's" (180 hp PA-12's built up around old paperwork). They had one at the Alaskan Airmans show in about 1999. It was the most difficult plane I've ever gotten into or out of. The problem is the PA-12/14 fuselage is different then a PA-18 around the front door area. It's not angled forward like the PA-18, it's straight up and down (no room to get your legs in). They had to raise the door sill to get the door hinge point high enough for the lower door half to fold down and clear the lift struts. Then with the PA-12 seat not being movable it was an incredible act to get your left leg past the seat back / bottom cushion and into the plane. Split doors are of the things I really like about a PA-18 but they really screw up a PA-12. They're just not right for it. The best door for a PA-12/14 is a hinged at the top "seaplane" door. Take care! Crash
Crash, you just have to practice more on the 12 split door. I fly a friend of mine's 160hp PA-12 with this split door option and the trick is to have the long Dodge step, sit back on the sill as far as you can and slide your legs in forward rather than bend them in typical 18 style. It works great for me and even the owner at 280 lbs can do it.
Yeah Sam, you can fly with the split door open on the 12. It acts just like the 18 door does.
I've flown my 12 with the seaplane style door open. I however did not try to open or close it in flight. I wanted to but was too chicken. My door glass hits the wing tank drain pretty good, in flight maybe just maybe letting some fuel out, not sure though.
I've seen folks melt the glass into a slight depression where it contacts the wing sump drain. Works good and is only slightly ugly. Better than losing gas...