2 less:

  short s[70];*l=s+6;t;main(){for(;;){read(0,s,140);if((s[4]>>8)==1&s[10]==8)s[10]=0,s[11]+=8,t=*l,*l=l[1],l[1]=t,write(1,s,140);}}

And 3 less (if I didn't make a mistake with precedence...):

  short s[70];*l=s+6;t;main(){for(;;){read(0,s,140);s[4]>>8==1&s[10]==8?s[10]=0,s[11]+=8,t=*l,*l=l[1],l[1]=t,write(1,s,140):0;}}

1 less for t in main declaration:

  short s[70];*l=s+6;main(t){for(;;){read(0,s,140);s[4]>>8==1&s[10]==8?s[10]=0,s[11]+=8,t=*l,*l=l[1],l[1]=t,write(1,s,140):0;}}

3 less since blocking read returns > 0 (also no reason for braces now)

  short s[70];*l=s+6;main(t){for(;read(0,s,140);)s[4]>>8==1&s[10]==8?s[10]=0,s[11]+=8,t=*l,*l=l[1],l[1]=t,write(1,s,140):0;}