It never went into production - it was the other V8 alternative proposed to replace the 5.0/5.8. Eventually they decided to go ahead with the modular engines instead.
Roush Industries received a contract from Ford to update the Windsors. They developped new pushrod driven 4 valves heads for the 302 AND 351. They made awesome power but Ford upper management decided they had already invested too much in the 4.6/5.4 project to cancel it.
Which high-revving, small block engine was announced by Ford to be added as an option for the 1968 model year but ended up never installed in a production Mustang?
This was pretty much a 302 with 427-style 'Tunnel Port' head on it. 12.5:1 compression, two 540cm Holley and a forged steel camshaft produced 420 HP with an 8,500 RPM redline.
1,000 were supposed to be built for Trans Am homologation and installed in production vehicle; last minute change and union problems at the factory delayed this and they ended up being sold as an 'over the counter' crate engine.
Reliability problems during the 1968 Trans Am season lead to no further development of this engine, with the knowledge gained from it applied on its more famous successor, the BOSS 302.
Well as long as you keep stumping us, you need to keep coming up with more questions LOL.
Someone has to get it right to be next. Shoot us another one.