You may indeed have a blown head gasket, but try draining the oil, replace with fresh and then retorque the heads. Many 91/93 164s end up with poorly torqued heads after many thousands of miles. I had the same thing with my 91S, chocolate mousse under the valve covers, but a retorque to the max level in the manual fixed it for now 80k miles with no problems.
If the retorque doesn't fix the mousse problem, then yes, the head gasket is leaking.
The other problem, of oil in the well, is usually a bad or misplaced plug well gasket under the cam cover. Easily remedied by either relocating the rubber gasket or replacing with a new one. Not a problem with head gaskets. Since you say the oil is bubbling, also check that the #5 plug is torqued to between about 18 to 24 ft-lbs, and that it has a proper ring washer under it.
The worst case for the bubbling might be a cracked head, but my feeling is that a cracked head is not that common. Hopefully, it's not that.
1989 Milano, Shankle Sport
1991 164S, stock
1994 164LS (~Q)
1972 Morgan 27
previously owned since 1964:
62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6