904 in 65 Valiant Signet (US Dart)

I am looking at getting a stall converter for my 65 Valiant Signet that has a 904 in it. It is the lovely ball and trunnion one... Anyways, when I was speaking to Mancini Racing they asked if it is 19 or 24 input spline. Any thoughts as to what it is and as well suggestions to up the stall from factory? The engine was replaced with a 1969 318 with a mild 340 cam. I have no idea of what the cam is...