The was a seat belt interlock in '74, but probably 99% were disabled by 1975... Search 1974 seat belt disable, should find all the info...
DELETING INTERLOCK FUNCTION Locate the emergency start override switch (under hood) and remove the 4-wire terminal connector attached to it. Cut the No. 32 circuit (RED/LT. BLUE) wire and No. 33 circuit (WHITE/PINK DOT) wire as close to the connector as possible. Using a butt connector, splice the two wires together and tape the splice to waterproof it.
Which wires? For the solenoid or alt.? As for alt upgrade I did large case 1 g. 100 amp. $45 rebuild off ebay. The guy was great