my.emask &= ~ENABLE_IMPACT;

Lots of little things change with the transition to Lite-C.

EDIT: You're also going to need to change a few of the flag-setting lines in the entity action. The good news is you can condense most of them down to a couple lines.

my.emask |= ENABLE_IMPACT;
set(my,POLYGON | INVISIBLE);
my.eflags &= ~(FAT | NARROW);