I wonder if a BMW engine from a RR 03/04/05 would fit??

Maybe, but then you may as well rebuild a Rover motor from the ground up, and still save some money.

dont know if you have seen this but its worth a read about the casting of the Rover blocks, just go down the page

http://cgi.ebay.co.uk/ws/eBayISAPI.d...Name=WDVW&rd=1

I just signed up for the forum, so I wasnt sure if you got this fixed yet. I experienced the same exact problem and purchased new exhaust manifold gaskets. However, it did not ifx the problem. The head gasket on the 4.0l is a bit thin from inner to outer wall and sometimes can get burned up. I just replaced my head gasket on the right side and sure enough I had a 1/2 inch gap from the piston wall through the to the outside which is just as a expected. While the engine is cold, try to see if the air is coming from beyond the exhaust manifold gaskets. Plus, if it real loud and higher pitched you can tell it is right at the point of combustion. If you are confident in working on your own vehicles, it is not that hard of a job. Take a weekend and save yourself the $1000 that a dealership would charge. I also bought my gaskets off Roverland in Florida from Ebay. They saved me over $100.

Got it fixed, the guy I bought it from offered to pay for half, and knew an out of work mechanic to do the job. My cost (parts and labor), was $324.

Good deal.

BTW, it was exactly as you described.