Yoshifab used to sell them, but stopped. Because it didn't make for a very good bolt-on solution.
1) There's a nasty round 8V runner to oval 16V port transition that leaves all sorts of nasty vertical surfaces hanging out in the airflow.
2) The intake manifold mounting surface on a 16V head is set over a couple of inches and angled up a bit more, so an 8V manifold bolted onto a 16V head still isn't a very good fit in a 240 anyhow - the throttle body still points *right* at the brake master cylinder.
Then there's the fact that the 8V intake just isn't really all that great for higher flowing higher HP applications anyhow.
That being said, I did use a Yoshi intake adapter on my first 16V build. But I did spend a bunch of time porting the head, the adapter, and the intake to make a smooth transition:
But spending that much time and effort on a 'bolt on adapter' kind of misses the point.
And when I got the motor back in the car, and the head on the motor, and the intake on the head....
My git-r-done solution was to hack a short 850 N/A 3" throttle body on, and to carefully bend over the brake line that was most in the way:
Still had to use a 'tight angle' elbow:
This ended up not being intended for pressure, but instead for a turbo inlet. On the dyno I saw it balloon outward a bit under full boost. Still worked fine for a couple of years. heh.
I also had to mangle with the throttle spool and bracket, because they would have been rubbing the hood.
CLIFF'S NOTES: Neat only in casual theory, in practical application not worth it at all.