Here's my story as the 3rd owner of my '72 Tii.
Original owner had put 187,000 miles on the car. He had installed a 3 gauge package on it and saw that he was loosing oil pressure. A friend who owned a BMW dealership told him that that he could get a new Tii engine built for him cheaper than it may cost to fix it. So in 1987, he installed a new engine. He then installed all of the original bits etc. Started the new engine and the pressure was low. He then changed the oil pressure sender and everything was fine. 15,000 miles later, he parked the car in one of his garages in the '80s until a friend talked him into selling it to him. He never drove it and I was able to buy it 6+ years ago.
I was then told that the original owner still had that engine sitting in his garage and he would love to have me pick it up. I did that and it sat in my garage for 6 years. I finally decided to rebuild and install.
After the machine shop got done and we looked at the original block, pistons and everything on the head, that engine could have been sprayed off and reinstalled with no problems.
So now I have an extra Tii engine built in '87 by BMW with 19,000 miles on it sitting in my garage.