I was about to post a question here when I finally realized the error of my ways, so I thought I'd post anyway in case someone takes the same path as me.
I'm converting some software from a QG8 to an SH8. I looked carefully at the ICS diagrams and the ICS registers. Yep, the same thing, so that part should be pretty much a copy & paste.
Uhhh, no. The DCO on an SH runs twice as fast as the DCO on a QG, and therefore the bus clock is 2x that of a QG. Two clues that I missed: 1. The DCO runs at 1024 times the reference clock vs 512 on the QG, and 2. max bus frequency spec on an SH is 20MHz vs 10MHz on a QG.
The simple fix is to keep BDIV at divide-by-2 and not change it to divide-by-1 like I was doing on the QG.
Think I've missed anything else?