Recently my original stereo on my 86 740 went out and I started looking at aftermarket options but I learned you have to bypass the original amplifier and I’m not that good and I’d prefer to have the original stereo anyway because I love cassettes. I started looking for factory stereos but none of them are my exact model. I’m just wondering how interchangeable they are? Has anyone done this or have any advice? It would be pretty rad to get one of the 780 ones with the equalizer too but I’m not sure how possible that is.

 

If you can find a good working replacement, it should plug right in.
The only replacement problem you may run into is that the OEM speakers are 8ohm and most modern stereos run at 4ohms.
You can get a splice harness and install kit from Metra for an aftermarket single DIN stereo

 

I'd start by checking out the crutchfield.com web site for options. Newer models often have more power in the head unit than Volvo did with their stand alone amps so it may be worth going for a complete upgrade.