There is not that much different...
...between a 6 and a 6A. The biggest question is how much work has already been done.
1. Drawing 28 shows the difference in the F611T (tail wheel) and the F611 (tri-gear) bulkheads.
2. Drawing 28 shows the difference in the F-612 Bulkhead.
If the fuselage has progressed beyond this stage, I believe you are still ok, but look into the tail tie down solution requirements.
3. The engine mount is different, you will need the nose wheel version.
4. You will need the main gear legs and the landing gear mounts. The legs and mounts are now match drilled for alignment.
5. You will also need 2 of the F6101 Al plates as well as some additional hardware. Check your drawings (or preview plans) carefully. You can find all the hardware buried in several different sheets.
6. And then you need the nose wheel leg, fork, pants, hardware, and leg fairings.
7. I believe the brake lines are routed different between the -6 and the -6A.
