As I was making these for a man’s foot, I increased in general by 8 stitches to 72 each sock. I added the recommended yarn-overs on rows 4 and 14 then dropped them on the next row right before the slipped stitches.

I worked toe-up TAAT with 35 st in the instep and 37 st on the sole. I omitted the purl stitches at the edges of the sole needle.

I increased the gusset until there were 61 total stitches on the sole. Then:

Row 1: k20, pm, m1R, k21, m1L, pm, turn
Row 2: sl1 WYIF pwise, p20, turn
Row 3: m1R, k19, m1L, turn
Row 4: sl1 WYIF pwise, p18, turn

Continue these rows until you get to:
Row 16: sl1 WYIF pwise, p6, turn

Then resume Scylla pattern at Row 13 as written.

The heel flap will be worked across 36 stitches rather than 32, so repeat the k1, sl1 pwise 16 times in total on RS rows and p33 (instead of 29) on WS rows.

72 stitches made about a men’s size 10. The slipped stitches don’t allow for a lot of stretch in the girth. For a men’s large I’d plan on 80 stitches.