Well, I have thought of a couple...
Due to the very-limited rpm range (less than 5,500rpm, tops,) the slant six turbo motor doesn't need a high rpm ignition system like a high-winding, 500 HP, normally-aspirated small block. A stock distributor will work fine, with no worries about effective spark at 7,000 rpm... 'cause, that boosted slant 6 is never gonna see even 6,000 rpm, much less 7,000...
Advantage, slant six
There are no aftermarket (aluminum, or otherwise) cylinder heads for the slant six, so the best you can do is to port the original head, and add some cheap 1/75"/1.5" valves (some folks have used 318 valves.) And, there's only ONE head to deal with, so there's just no place to spend money (of the quantity the V8 car can absorb) on the head. A complete ported head for a slant 6, ready to run, will be cheaper than a pair of aftermarket V8 heads that will support 500 horsepower, I believe.
Advantage, slant six
Now, I really AM done!
I hope that after reading all this meandering set of posts, I have made a case for it being actually cheaper to build a 500 HP turbo slant 6 than it is to make the same amount of power with a normally-aspirated, small block V8.
Thanks for listening!:D
