The Wayback Machine - https://web.archive.org/web/20170328173210/http://automotivemileposts.com/tbird1961specifications.html
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Automotive Mileposts  
1961 Thunderbird
Specifications

1961 Thunderbird script
ENGINE CODE

R


Z


390 Cubic Inch V-8 (275 Horsepower)
  4-Barrel Holley Carburetor/Dual Exhaust System
  (Export only; low octane)

Thunderbird 390 Special V-8 (300 Horsepower)
  4-Barrel Holley Carburetor/Dual Exhaust System
TRANSMISSION CODES

4
Cruise-O-Matic (Automatic, 3-Speed)
REAR AXLE CODES

1
3
6
A
F
H
2.91:1 (Also listed as 3.00:1 and 3.56:1)
3.10:1
3.00:1
3.56:1 Equa Lock
3.56:1 Equa Lock
2.91:1 Equa Lock
WHEELBASE

Length
Width
Height
Weight
113 Inches

205 Inches (Overall)
75.9 Inches
52.5 (Hardtop) 53.3 (Convertible)
Hardtop: 3,958 Pounds
Convertible: 4,130 Pounds
About early 1961 Thunderbird production...

It is interesting to note that a few light-colored, very early production 1961 Thunderbirds left the factory with light gray rubber gaskets between the front bumper and fender, as well as between the rear bumper and quarter panel. Black rubber gaskets were most frequently seen during most of 1961 production.

Ford also installed a few radio antennas on the left front fender instead of the more common right fender, and a few cars apparently even left the factory without the rear quarter panel chrome "spears". For some reason, relatively fewer 1961 models have survived over the years, compared to the 1962 and 1963 models, making them somewhat rarer today than their counterparts.
1961 Ford Thunderbird Hardtop shown in Corinthian White
Hardtop above shown in Corinthian White