Most people build the S-1 over the S-1A because it is OTS eligible. If you can't find S-1A plans, perhaps you can modify the S-1 plans. I know the "A" used LE sheeting and a plastic canopy. Not sure of other changes or "improvements". BTW, the kit came with isometric views and assembly instructions so you could not use the plans to build from.

Good luck.

George