Hi Vido. I think '74 North American spec. X1/9s - without a/c - came with a Bosch 33A alternator. I think by '75 they came with a 44A Marelli unit. I dont know if they are physically interchangeable (that is if the brackets were the same), but I do believe the wiring was different and require a different voltage regulator (which in those years was external).
So....if your X has the Bosch unit, probably best to stick with that. 33A should be more than enough for your purposes. You would only need more than that if had some huge stereo, or a bank of extra driving lights. Or drove lots at slow speed in a snowstorm with wipers/rear defogger/heater/lights going full blast.
Yeah, you could try to rebuild yours. But would likely need at least brushes, bearings, diodes, etc. - if you are lucky.
And yeah, you could take it to a local rebuild shop. But for a thorough job there, gotta be at least $100.
But....in reality....I think your best option is to just poke around the internet for a rebuilt unit. Like here:
http://www.rockauto.com/en/catalog/...104893,electrical,alternator+/+generator,2412
Only $50 for a fully rebuilt unit
Or here on Ebay for $80:
http://www.ebay.com/itm/FIAT-128-X1...ash=item21055fe784:g:-v0AAOSwo0JWQSnQ&vxp=mtr
I'm sure if you poke around enough, you could find even cheaper !! Prices seem to vary a lot.
Compare carefully the pics of anything you buy, to your existing alternator, to see that they match perfectly. Note most rebuilt units come without the pulley, fan, and condenser. These will have to be transferred over from your existing alternator. Which is another reason to stick with the same Bosch or Marelli unit you have currently.
Hope this helps. Cheers, Doug