Putting shims on a 912ULS head

You should be good. 
Those shims should lower the compression ratio to slightly less than the 80HP 912UL

If you didn’t install oversized O rings you could have some oil leaks.

Ed

Hi Phil...you can find the formulas online.  Here is an article on how to do it for an automotive engine, same process.  

https://www.motortrend.com/how-to/calculate-compression-ratio/

Cheers

Interesting matter. Found this calculator online:

https://www.bgsoflex.com/crchange.html

Example: if one lowered the compression ratio of a 100hp engine with CR =10.5 to 9.0 the reduction in hp will „only“ be 4%. That to me does not sound too significant.