All this information is from a post by SlantSixDan on slantsix.org
http://www.slantsix.org/forum/viewtopic.php?p=208914&highlight=external+filter#208914
The 1960-'63 Torqueflite automatics used an external, in-line transmission fluid filter as an optional accessory in '60 and '61, standard equipment in '62-'63, not a flat in-pan filter such as the 1964-up transmissions used. In place of the in-pan flat filter, the early cars had a metal screen. If your car is so equipped, you will find the black, canister-shaped filter clamped to the engine block right at the level of the oil pan rail, below and ahead of the starter motor, with the trans fluid pipes threaded into each end of the canister. These canister-type filters are no longer manufactured. New Old Stock items can sometimes be found, but are usually quite costly. A replacement for this canister-type filter can be had (while supplies last, which won't be long) from Pat Blais,
[email protected] . You can without much difficulty convert to the '64-up in-pan filter, making future transmission service easier and less costly.
There are a few different in-pan filters that will physically fit, but on a pre-1966 transmission, you need a filter with two fluid ports in it. The '66-up filters have only one, and if you use them on a '65 or earlier transmission, you'll starve the rear pump and damage it; it'll get noisy.
For this project, you'll need:
•A 1964-1965 transmission filter (with two ports). NAPA or ATP 19715 or 17956 trans filter/gasket kit contains the 2-port filter. Other numbers include Wix 58656 and Fram (yuck) FT-1015A.
•A 1964-up transmission pan or a brand-new pan. Nice new pans with unwarped rails can be had from the dealer under p/n 52118 779AB, and they even include a spiffy magnet to catch metallic shavings. Whether you go that route or install a used '64-up pan, save yourself a bunch of current and future hassle: Discard the floppy cork or rubber pan gasket that comes with the filter kit. Instead, from the Chrysler dealer get the really nice double-seal, reusable rigid pan gasket P/N 4295 875AC. (Note these part numbers are for A904 transmissions, which have a roughly square-shaped transmission pan with one corner cut off. The larger A727 transmissions use a different pan and a different pan gasket.)
The reason why you need to change the pan is that when they changed to the in-pan Dacron filter for '64, they put a circular depression in the pan to provide sufficient clearance between the pan and the Dacron filter, which is thicker than the '63 and earlier pickup screen. This is why my '62 has "dropout" problems when cold (Dacron filter w/'62 pan); I really need to fix it 'cause it's not good to starve the pump for fluid like that.