1975 was, as I recall (but I could be mistaken) a transition year (from the 140)for a lot of the parts of a 240. Of course, it's been a long time and I could be mistaken, but just a few cautionary things come to my mind that you should confirm by other sources:

The wheel offset may be different than later model years -- and I think the front antisway bar might need a configuration (to fit around the pushrod engine) that is different than for later model years (which fit around the red block).

The fuel tank probably (if it hasn't been upgraded) doesn't have an internal transfer (a.k.a., intank) fuel pump -- if you keep your fuel injection then you might want to upgrade that to forestall a lot of vapor lock issues in warm weather (I have personal experience with this in a '75), although it might not be necessary if you use the webers because they require less fuel flow.
Also, if you don't upgrade to a transfer pump and keep the tank OEM, you'll want to stock up on Volvo's remaining supply of fuel strainers that go behind a little plug (internal ~1/2" square drive -- I slightly ground down a half-inch socket extension to fit) under the fuel tank (accessible from beneath the car).

Also confirm what brakes you have. In later 240s there almost universally Girling front and ATE rear, but in '75 you might have ATE fronts, and their pads and hardware (springs, pins) are hard to find, so stock up on supplies; ditto for the front rotors. And I'm not sure whether you can swap in later 240s' Girling calipers as bolt-on replacements.
However, I think that you can upgrade to 164 (of only that same '75 model year) front brakes (vented rotors) if you can find a good set in a p-n-p (or in the for-sale pages of Rolling).
Fortunately, I think the rear brake hardware will be the same as for all later model years, so no worries there.

Anyway, these are from vague recollection, so confirm elsewhere to be sure. I wish you good luck, and lots of fun :-).