S3 2+2 center of rotation

[JohnnyJag (John Baker 1971 Series 3 2+2)]

So. 71 Series 3 2+2
I’m fabricating mounts for a rotisserie. I’ve got the monocoque level based on the sills and a frame built for the front end. Boy is it great to weld good clean steel with a quality welder.
Can anyone give me an idea of where the center of rotation might be for the entire monocoque?
I’m going to be building the structure for the rear tomorrow. I’m planning on coming off of the rear IRS mounts, under the boot and having a minimal plate where the license plate mounts. I had considered mounting through the hatch in the back but I think that I’ll get better support this way.

[Harvey_Ferris (63 FHC 67 2+2 newhillgarage.com)]

For my S1 2+2 I mounted as shown in the photos. I couldn’t swing it with one finger but it rotated OK. My arrangement had one problem. The forward sills (like at the battery) hung up on the engine stand so I couldn’t fully rotate the car.