That is the o/d 4 spd auto - you can use a toggle switch to engage the o/d - just be sure to ground the wire fron the tranny that would go to the temp sensor for it to engage. Is that a narrow block or wide block tranny - they came in both in 87? BTW - that has a screen for the filter inside the tranny - just take it out and clean it - its reusable. My Dad had the same tranny in an 88 ram 50 and he couldn't kill the tranny, even after he tried to drown the truck twice driving it through water up over the hood. That truck had 160k when I sold it and it still ran strong.