Ive got a 75 with only 75000 miles...unheard of, huh?  It's a little screamer as it is, but I'd like to know if anybody knows of anything I can adjust or tinker with to get more from it?

No not really some put headers on but I don't think it helps.  Most people go to a more moderern engine to get more power or go to a small block v8. 

Lance

For ease of operation and good power, grab up a Weber DGEV 32/36 carb kit for $300 and bolt it on.  Also they make headers for it and cost $200 to you.  Install a later 620 matchbox electronic dizzy.  Since its an L20B motor, you could go further and install a ported A87 peanut head shaved for higher compression and install a NISMO performance cam.  It would be a really smooth screamer.  You have lots of options if you want to stay stock 4 banger.