The pattern can be enlarged by using a heavier weight yarn and/or slightly larger needles. To estimate size do a large, square swatch in rib, eg. 40 stitches, and stretch it to see how large it gets (a comfortable stretch). Measure the with, and calculate how many stitches you need for an inch. Do this until you find the yarn/needle combination you need to follow the pattern. This would be easier than trying to fit the lace pattern into a different number of stitches.

For a 40-43 inch chest use a 3 ply yarn like Drops alpaca, and 3 & 3.5 needles.

I discovered an error in the vest pattern. If you knit it flat (back and front separately) you’ll need to cast on 122 stitches for both pieces, otherwise the lace pattern doesn’t fit in. The lace pattern has repeats of 12 stitches + 2.

If you knit the vest in the round you don’t have to add stitches as you can go straight to the pattern repeats which will then add up nicely.

The entire lace pattern including the shaping of the points at the top of the vest are written for a 122 stitches cast on. If you are knitting the top in the round using 120 stitches per side you’ll have to cast off 3 stitches at the start of the shaping of the under arm area instead of 4.