Just to make sure you got the correct filter in the box...here's the diametrical info on the correct filters for the 235/261 engines...
the would apply as long as you still have the original filter can.... If it was changed/swapped at some time...then it'll be a trial and error as to what filter you need...... but you can also look as most all canister style filters are stamped with their number...

The diametrical difference between the Fram C21(P) and the C4 filters is as follows;
Outside diameter C4- 4 5/16 and C21P- 4.5 inches
Inside diameter C4 and C21P both 9/16
Height C4- 4 13/16 and C21P- 5 inchs
Gasket number(Fram) C4 151915 C21P 125405
Gasket dimetions
Outside diameter C4 4.75 and C21P 5.128
Inside diamter C4 4 11/32 and C21P 4 3/8
Thickness C4 1/16th and C21P 3/32nd

The Fram C21(P) interchanges with the AC115 and WIX 51100 and NAPA 1100 filters
The FRAM C4 interchanges with the WIX 51006 and NAPA 1006 filters

Hope this helps
Michael

\'48 chev 2-ton boom truck (Boomer)
'49 Chev 2-ton flat bed
'65 Chev 35ft school bus
'88 GMC 6500
'72 Superior 26ft class "A" coach
'50 Farmall "M"
'71 MGB GT
'68 Austin-Healey Sprite
'65 Austin-Healey Sprite
and various other odd British cars
and lots of old radios.....

Although we know what the speed of light is..... What I want to know is... How fast is the speed of DARK??