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As long as the flash can be trigged by the PC-socket on the lens they should work.
If they don't have any automatic mode you will have to calculate with the guide number to get the correct aperture.
You won't have any TTL if you don't use the Metz that are compatible with the 503-bodies, ELX/ELD and 200-bodies.
Example of flash is the Metz 45 CT-4 (which was modified and sold as the Hasselblad Proflash 4504)
But some flashes have an automatic mode which makes the some kind of half automatic (compared to TTL).