Ford not Rover
All this stuff about the delightful Rover / Buick 215 ci V8 family is music to my ears, as is the exhaust note of that emininetly practical and tunable engine itself. But with regret I must confirm that the one-off Aero Bonner Sapphire engine powering the converted Chipmunk, as written about in Pilot (still have it at home somewhere) was not based on the Rover but a Ford V6 block. It was quite clear in both the text and pictures.
I have no idea why he chose the Ford, since the Rover seems like a more practical starting point, but there it is. However, it was turbocharged, and knocked out some 200 bhp, looked like a mini-Merlin and gave the Chippy a nice pointy nose, with a little radiator underneath like a small version of that on a Hurricane. I'm pretty sure it was G-ARWB.
There may, of course, have been a different Chipmunk conversion at some stage using the Rover / Buick engine, but I've never heard of it.
Anyone know what became of Bill Bonner and his enterprise?