I thought I checked to see if the output shaft was locked. I had a trans rebuilt as I was driving mine, found a shift arm like mine and had them put it in (you have to remove the valve body to switch arms). I modified the shift linkage but it looks like I wasn't in park, I fired it up today for the first time (rebuilt motor too) and as I put trans fluid in it wanted to lurch forward.....but I had the parking brake on and wheel chocks .

Here's what I have, I think I need to go back more: