A/S did not give a GVWR for any year prior to 1994. Only a dry weight. Your dry weight was 4180 #'s. So load up your trailer and tow it to a scale. In Bend there has to be a truck scale some where in the city or may be Redmond up and down the 97.
There is one listed below which is a trek.
PILOT TRAVEL CENTERS109450 HWY 97CHEMULT, OR 97731
1966 Mercury Park Lane 4 DR Breezeway 410 4V, C-6, 2.80 - Streamless.
1966 Lincoln Convertable 1971 Ford LTD Convertable Phoenix ~ Yeah it's hot however it's a dry heat!