That's what I bought first and sent it back. The width was too great, to fit between the firewall and the twin sticks. The length was perfect, but I couldn't shift the transfer case. You're using the vacuum shift, so might be alright. Are you sure the height will not interfere with the vacuum handle?
One other thing, just my opinion here, I think the old air system is not up to grade with the Restomod system. Seems the quality isn't the same.
I'll try to find a picture. Here's some with it to the far left.
You're correct on the front to back and length being left to right. I am using the H55. The height might be an issue, also. Not a lot of room up there for hoses. etc. On the quality part, just seemed the evaporator and vents were made with cheaper materials. I felt that way, before I bought the Restomod.
I got burned on the return. Shipping was high and they charged a restocking fee. In my mind, worth it to get the other one.
Edit: I'm remembering now. I had to go that high in order to clear the transmission boot. I'll see if I have more picture.