Just add "max=cur" and both lines are printed out as you want.
Code:
awk ' BEGIN { OFS=FS=":"; cur=max=0; seen=""}
{
cur = length($1)
if (cur > max ) {
seen = $1 " " $0
max = cur
} else if (cur == max) {
seen = seen "\n" $1 " " $0
}
}
END { print seen }' $INFILE
