ST400 filter is different. WIX part number 58879, or equivalent, is what you need. My local Oreilly's was able to get it in stock the same day.
After some checking, I have found there is an idea out there that the 1966 ST400 uses the same filter and gasket as the 1966 TH400. But there are several other folks who tell me it is a different kit than the TH400. I have seen the one that CameoInvicta was king enough to reply with but wonder if the specific 1966 ST400 has any differences. Would the pan shape tell me one way or another as to which kit would be the best bet???
All you have to do is look at the valve body. The later THM400 used a flat filter that used a shouldered bolt that threaded into the valve body. If there is no threaded hole in your valve body, you need the filter that was pictured in the 2nd post. It is possible to drill and tap the hole for the later filter. BTW, the ST400 was just Buick's name for their THM400. From 65-67, the ST400 was a switch pitch. The pan gasket is the same. The ST400 pan however has 3 dimples, and a shoe heel impression where the filter picks up the fluid. This article shoes the pan I am talking about. http://www.buickperformanceclub.com/switchpitch.htm The picture below shows the bolt that secures the flat style filter.
