wwall: Looks like Marshall gets in trouble with 19...Nh8. Perhaps 19...h6 or 19...Nc6
After 20.Nge3 c6 looks too slow. Perhaps 20...Nc6 or 20...Qd8 or 20...Bxf5.
After 25.gxf4, White threatens 26.Nxe7+ and 27.f5. So instead of 25...a4?, perhaps 25...Nc8.
After 26.Nxe7+, not 26...Nxe7 27.f5 traps the Bishop.
28...d5 doesn't seem to help. 28...Bc8 or 28...Ne5, but White is winning.
Instead of 30.exf7+, 30.Qxf6 Qxf6 31.Rxf6 fxe6 32.Bxe6+ looks stronger.
Instead of 35.Rf4, 35.Rd1, threatening 36.Rd7 looks strong.
Instead of 36.Rg4, 36.Rxf6+ Qxf6 37.Rf1 looks better.
Instead of 47.Qb3+, 47.Bxc6 Nxc6 48.Qxc6 looks strong.
Instead of 50.Bxg4, 50.Qf3! wins the knight.