Yes, its true. That and a number of Prior, Kieft, and Hercules, even Progress scooters. The Schmitters were veracious engine nappers, and still would be if the economics were right. I myself had the remains of a Prior not 4 years ago and supplied the dead bike on to a scooter collector building a bike out of rubbishy stuff. I kept the engine parts as I wanted a set of casings for my second KR201. The taped holes under the engine, I argue, were used for an extra middle mounting to stop the long optional extra Roadster exhaust from working loose. My original KR201 has this on it, along with the tripod rear tubular mount. If it is not original, then it should have been, as Basil said it worked. He serviced the Vicar of Bampton's KR201, which had the same thing, and he reckoned this was the fastest Schmitt he ever drove.
Some Nobs reappeared with alternative engines. I had at least two that had Heinkel engines put in. Not daft as later those Fulda licences that chose, did exactly that. I am not sure it is not a better car in that form. However it was not done with 175cc or modified scooter units as were these. Hienkel 175cc units are still cheap today. One roadworthy car I had even had a front spoiler to handle the, alleged, extra speed. That car did Faringdon to Kemble Airfield every day, 54 miles, for a few weeks, not without its problems though. Seem to recall swapping it for the Goggo Shopper I owned 4 times. That also did the F to K commute for some 4 months without a hitch.
I also had a Nob with a Villiers 250? in. I say that as it had a decompressor. This used to overheat as I think it was a Bond engine made for the big grin of Preston, rather than the confined rear cheek of a Fulda. I also had one with a 250 Villiers twin out of a scooter. That had potential, but was fitted rather badly. I believe that car was eventually restored, with another stuffed one as donor, into a prize winning example by someone from Essex/Suffolk way. I do not doubt the engine survived and might be in a suitable home too. So its not all bad news (Richard).
What about a Bruetsch Bussard with a Blizzard engine? Thats just silly. Is this Bussard what became the Spatz (Sparrow I believe)? Mighty are the fallen, in name.