EJ20D vs EJ251

I’m looking to fix up a 03 Baja for my daughter; the car runs but has a knock a 320k miles.

I’ve been searching through the Jdm sights for a replacement engine.

I keep seeing the EJ20D DOHC engine with an automatic transmission with the correct final drive ratio almost the same price as EJ201, which is supposed to be a pretty much drop in.

My question is would it be tough to put the DOHC engine in.

I’m very capable of changing and modification if needed.

I keep searching and can’t find a definitive answer.

Correction, it's an EJ204 and automatic transmission I was looking at.