I responded about frame cleanup in your other thread. This engine's mount brackets are close to the front of the engine versus the 3.1 engine brackets which are more rearward. Rather than hacking something up I chose to just start with clean rails "a clean slate".

I did a few measurements on the old engine and bellhousing along with the new one and learned a few things:

-The old bell tapers off more gradually
-The new engine is shorter in length.
-The old engine had a lot of space between it and the firewall.
-I am going to have to cut up my tunnel and part of my firewall anyway to fit the raised drivetrain.

So I realized I could be more riskier with mounting the engine closer to the firewall.

On my truck, the firewall was in-line with the passenger side bracket on the framerail that holds a fuel or brake line I forget which, maybe fuel tank vacuum. Either way I just lined up the back of my engine with that. I figured wherever the shifters ended up would be ok since I am going to have to build a new floorpan section anyways.

Since I went with the dual cases, have no problems cutting the sheet metal and moved the engine back, I wanted to mount the axle in the stock location. It ended up about 3" forward at full compression because the further back I mounted it, the higer I would need to lift the front end since my shackles are through the frame. My goal is to keep it as low as possible for CG and legal issues. With the shackles in the rear and use of Zu rear springs, the axle moves a lot during travel I would estimate 8" forward on full droop and 3" forward on compression. Actual numbers will be less in the real world. Hope this helps sorry about the novel.