@FR85
https://www.fdricambi.com list engine lid hinges for the 600 but they might not be correct for your car (+ they cost £70 each
).
I rebuilt a 1968 600 and if I remember correctly, (bear in mind, I'm trying to remember from 45 years ago) mine had the top part welded to the body and the longer bottom part attached to the engine lid by studs and nuts?
Have you considered an alternative hinge? Maybe outer door hinges as used on the Mk 1&2 Mini's could be used? see
https://minispares.com
(>body>doors>fixings, then go to 2nd page)
If you
really wanted to save time/money, you could even modify ordinary shed door 'T' hinges to work (if you're not bothered about originality).