Euro '83 635 CSi manual production date 11/82.
It had been running at 1/3 normal operating temperature. Water pump had been spewing for some time as evidenced by dried splatter marks on hood and coolant under the weep hole. Installed new waterpump, thermostat, new hoses, and cool blue...
Some steam from exhaust at startup. Ran at idle for 20 minutes bleeding system. Temp needle went 1/8" past halfway but never more. Never actually drove the car at that time. Checked under oil cap: very light swirling milkiness evident... Car sat for one week.
Drove the car yesterday... Some steam from exhaust at startup; went away after a few seconds. Drove for maybe 4-5 miles. Left idling for a few minutes; steam not billowing but still there. I noticed a gentle misfire accompanied with a puff of steam. This symptom was also evident at idle. Temp guage at normal. Shut off engine. Checked under oil cap: even milkier than previous. There was no evidence of oil in the coolant. Dipstick did not have any foam or milky color to the oil drips. Have not pulled plugs yet. Car is sitting waiting for the head to be pulled... I plan to replace the head gasket and replace whatever may be necessary on the head itself; if it is still useable. Will examine block/bores as well.

Man, am I glad I have not sold the 540...

Question: If I undersand correctly; the euro motors are a 10:1 Compression Ratio. The US models were somewhere in the 9:1 range. Was this accomplished with different pistons? Real OEM gives the same part number for the head gaskets and cylinder heads themselves between US and Euro M30B34s. What differences between Euro and US motors should I be aware of during the process of repairing the head and replacing the gasket?