In a nutshell, you’re going to have overheating issues if you don’t move your engine significantly forward. I’d recommend 3”+ based on my experience. If you position it right, the front and rear driveshafts will be the same length. If mine was about a 1/2” inch further back they would be the same length.
Starting at post 22 are pictures and measurements of my setup.
forum.ih8mud.com
I kept my engine much lower than most. Had it been 3” from the firewall, I could swap my rear shaft that is starting to have play in the splines for the front and be set for another 30 years.