I think most folks on this site want to keep the old style inlines because they're not new. It's like collecting antiques. But with motors.
Could I have swapped out my 250 for a 350 for the same amount as I have in my 250? Yes. Why didn't I? Because the engine came with the car and every car show I go to my car is the one everyone gathers around. Not the blown LS 68 next to mine. My little inline. It'll be doubly so now that I have a bit more chrome, 3 more barrels, and an extra inch diameter exhaust.
Why bother swapping engines at all when you can just go out and buy a new Camaro with 400+ hp off the showroom floor? Why stop there? There's a couple of supercars now with over 1,000 hp and a warranty! Heck why even stick with wheels at all! Let's just all buy jets! They're even faster! Heck why even stop there! Just buy a rocket and go into orbit!
To each his own but I'm sticking with period correct stuff on my little 68 granny car. I'm happy with the unique sound and feel of the old inline.
