I decided to use the sleeve ruffles from the Larkin & Smith English Gown pattern. I cut the ruffles a little longer as indicated in the pattern and narrow hemmed them, stitching them on the gown using the techniques described in the pattern.
I cut crosswise strips 2 inches wide for the trim and roll hemmed the long edges. I pinned the strips over the ruffle stitching in box pleats approximately 1 inch wide. I didn't measure, just pinning the pleats and adjusting them so they looked even. I used a prick stitch to stitch the pleats down about 1/4 inch from each edge.
I made the same trimming for the neckline. I used two full widths of fabric and started at the center front, pleating around to the back.
I was very happy with the outcome of this upgrade--particularly since I know it is now historically accurate! I wore my gown with my new mitts and tambour embroidered apron to Mt. Vernon on July 4th.