The reason is because Chrysler had terrible machining tolerances when it came to deck heights that were too tall and combustion chambers that were too large and pistons that sat way down in the hole at TDC.
We used to intentionally run the mini van heads on the fat side for the head faces. That way if we had to reuse/recycle a head and it got the block face scratched, we would do a clean up mill cut to get rid of any nicks and scratches that may have gotten on the heads. We ran them as a batch job when we got enough saved up....
Running on the fat side gave us the ability to recondition any heads that may have gotten some scars or scratches so we could reuse them. Otherwise, it would have cost alot of $$$ to have them scrapped....
