Old BMWs are particularly easy and common for swaps since many of the parts across models and model years are interchangable. The swaps used to be mainly to newer BMW engines or to LS* engines, but there are a few people doing it with Tesla and Toyota parts now.

It's rather interesting from a hacker point of view -- these guys are analyzing the CAN bus signals and checking components with oscilloscopes, then building their own circuit boards to connect and manage the various batteries, inverters, and motors. Check out:

https://evbmw.com/

https://www.instagram.com/teslified_e30/

https://www.instagram.com/tesla_bimmer/

Disclaimer: I'm an E30 owner myself.

I don't know where you're located, but in Australia there's a handful of workshops that'll convert a classic car to electric.

e.g: http://ev-torque.com.au/ https://www.evmachina.com/ https://www.ozdiyelectricvehicles.com/ https://www.evclassic.com.au/

Enthusiasts have been fitting electric drive systems to older vehicles for decades.