It's no wonder the Slant 6 is so great!

4 mains is a weak point being the crank is 85 lbs
The head isn't designed for much bigger than a 170/198 cid.
The upgrade parts are pricey compared to v8... the trans needs upgrades from v8 versions once built up... the cheapest intake is around 400+$$$...

They are great... for running along time and getting ok mileage. That's it.