The only pair I could find for the front of my 67 Imperial were KYB I believe. I could no longer get Monroe or Gabriel. The KYB are definitely stiffer than the others. If you are in the Los Angeles Area I get them from a place called Olympic Distributing but they had to be ordered.
Their number is 323-732-3955.
The rears I put on are Monroes and I am happy with them.