For my coupe I replaced the seats with ~74 Firebird buckets. I had to modify the rear mounting but man were they comfy! I made my own extenders and I also put in a small diameter TA steering wheel. So at any rate that made the car comfortable to drive for guys too long in the leg like me.

I don't believe you will much success at lowering your seats with the existing seat mounting hardware.

However, I agree with others that installing the seat extenders and/or a smaller diameter wheel could be enough to make it more comfortable for you.

For the few drives I made with the vert (before tear down) I was able to got in easily because the top was down.