You may well have loosened some crud that clogged the purge line. Check it. If you don't know what or where it is, do a search for it.
It is almost certainly a head gasket with those symptoms. If you are going to drop the drivetrain yourself, you may as well Timesert it and replace the head gaskets.Now it starts a little rough but smooths out and drives just fine it just loses coolant out the overflow.
The n* is self purging of air.The system could be airlocked, you may have to "burp" it.