@flatbill Probably the Body & Interior forum would be best. I'll move this there for you. The part of your post describing what you did today is fine here. The technical questions need to go in a technical forum. I can't help with your question because I have 0 experience with it but it looks like you're on the right path. Hopefully someone with the answer will be along soon.

The key pieces in replacing the top are:

1. The slats and wood structure to support them and nail or staple to. You already have them.

2. Support between the slats so the top material does not sag showing the form of the slats. Hardware sloth was used if a radio was to be installed as it served as the antenna. Otherwise burlap or canvas or other material was laid over the slats and attached around the periphery (edges) to keep it in place.

3. A padding material was next to permit a little flexibility and "fluff" to the look. Old blanket, cotton batting or similar material will do the job. Don't make it too thick as the final look should not be puffed up just cushioned.

4. Finally the top material was stretched over the top and stapled or tacked in place. It is best to start in the middle of each side and work toward the corners. There are upholstery pliers to aid in the job but hands and fingers can work okay. The final top material needs to be taut so it resists flapping which can result in early failure. It is also best to put the material in the sun to heat it so it can be more easily stretched. Don't let it get so hot you can't touch it or pull it taut. Don't scrimp on tacks or staples. There can be a space between them maybe ~ 1/2" apart (width of a staple or so).

It is not tough to do singly but two is far better. One to stretch and the other to tack or staple.

@chip Thanks for the helpful info.  Billk