Is it possible to interchange side indicator lens - and any other parts, for that matter - between a Volvo 240 & other older model Volvos from the same era?

 

US model volvos generally didn't have the fender side indicator lamps. easy enough to install on a car without them, just need a hole in the fender for the wire, they are wired to the front parking/turn signals generally.

or do you mean the turn signal / parking lights ? those are model and generation specific. old 240, late 240 w/ tv panels, old 740, 1990 740, 1991-2 740 + all 940, those all used different turn signals.

'or other parts' leaves a big range of stuff. all the b230f engines with LH2.2 (85-88) in 240 and 740 are pretty much interchangeable, as are the b230f 1989+ w/ LH2.4 from 240/740/940 the 240 and 740/940 used different distributors and ignition systems, but you can swap them. mechanically, the engines were the same between 2.2 and 2.4, the differences were in the fuel injection, timing, ignition, so you can swap all that stuff.

AW70 transmissions used on non-turbos after about 1984 should all be compatible, EXCEPT, the LH2.4 1989+ cars require a notch in the bell housing for the crank position sensor, which the pre 1989 cars didn't have.

LH2.2 ECU are mostly interchangable with other LH2.2, and LH 2.4 are interchangable with (most) other LH 2.4. 240's used different ignition control units. oh, some 740/940 use Regina/REX, thats completely different than Bosch, and was never used on a 240.

the 240 rear differential has different hard points on it for the torque arms and mounts, so to adapt a 7/9 rear end would require some serious welding work, not worth it.

740 and 940 had larger front brakes with 15 or 16" wheels, while 240 was 14", so you can use 7/9 wheels on a 240, but not visa versa. also, 240 ABS only allows some 14" rims, not all.

interiors between 240 and 7/940 are completely different as are most of the electrics, fuse panels, relays are all in different places etc etc... early 240 had a different incompatible dashboard with late 240s. 7/9 seats won't fit in a 240, the bolt patterns are completely different.

very early 'flat hood' 240's had rather different exteriors front and rear. no body parts will interchange between a 240 and a 7/9, the chassis are completely different.

having typed all that, your question is really too vague. what specifically are you looking at ?

 

I put S60 side markers on my 240