Think about what you would do to a 240-Z, even V8 swaps - I think THIS is the most correct with what is out there today, even though I am not a fan of long crankshafts:

~ and I am a "Mighty Car Mods" fan, I think they hit it perfectly with this project

* You can look up the "BUILD FEEDS" from how this began to see the fabrication issues


Can you even imagine driving a 400 Horsepower 240-Z???​

 

Been involved with a couple V8 conversions (Chevy & Ford), even a mild build on the engine makes for a serious performer.
IMO, today: The place to spend the $$$$ is in chassis stiffness, suspension, & getting enough rubber on the ground.

 

When I was in Washington state - the guy who stored his car next to mine had a V8 Z. The only thing about that conversion I have reservations about is that it makes it considerably more nose heavy than the stock engine. The other side of that coin is more power especially if turbo'd, and V8 and I4 engines have a higher rev limit than a six. Something to do with crankshaft harmonics.

True 4 valve per cylinder heads for V8's are also seriously pricey at this point too, as far as I know

Q: Was the Mazda B2600 engine a DOHC? If so it's a four cylinder that could out perform the original 260Z and 240Z engines, lighten the car below stock, and leave a ton of room under the hood for turbo plumbing

*Stock L24 through L28's were I6, SOHC 2V

 

I used to play with the 280 Z's
The six's would scream with down drafts and headers, but putting a efi 5.0 with aod transmission in there made for a screamer.
You couldn't keep rubber on the back tires

 

The 5.0L can be set in the engine bay in a true Front/Mid Engine configuration.