Bill, The V12 is the same length (or about) as the 235 in my truck! It is 6 cylinder's long. Now it is wider, but that I have room for.
As for the in-line 8.... It is two cylinders longer. With a bore of 4" and wall thickness, cooling jackets etc. that probably puts us up around 10-12" longer than the V-12 or the 235.....
I run a fabrication business and have been stuffing things in were they don't belong for many years. I know how much work is involved. I am a body man as well as a welder/fabricator. I'm more concerned with the length over the width.....
Looks like the "Twin-Six" will quickly get outside of what I am willing to pay. I may start looking for a GM 503 six cylinder....Or if the right 235/261 comes along I will snatch it up and focus my efforts onto something else!
