Vivitar mid 80's made a family of flash with a dedicated minolta module (DM/M I recall). The module would clip onto the bottom of the flash, and had the shoe to interface to all the right camera hot shoe pins.
They also made a module to allow you to 'split' the flash. It allowed the head to be extended up to 1m beyond the camera.
The only place I have ever really needed off film metering using the above rig was when using a slide duper backlit by the flash head somewhat diffused
As long as the flash shoe has it's own sensor, you come close to off film metering by putting the sensor at the top of the camera.
Once you move into using multiple flashes you buy a flash meter, and forget all the hype about TTl flash, and wonder why it was such a big deal to you at the time.