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All I can relate as an A-B comparo, is my recollections of two conversions I did in the past.....the first was to an old Pontiac Lemans/GTO....picked up about 100% in responsiveness, and 3 mpg...not too shabby, did that one in my garage letting a machinest welder do the intake conversions....
NOW, the '72 L48 dead stock fresh engine vette I now have, grew a MAP version L98 injection, like '91 F'bird.....and lemme tell you, the instant change was astounding....
doubled the fuel economy, and it WAS in 'tune' before....went to ~24 mpg on freeway....18 around town.... and Jeezus, what a differance in performance...
now with the open ported 355 hotrod roller engine, and the o/drive auto, instead of the original muncie...the thing gets about 20 on freeway, and 16 or so around town...and my toes are heavy, most of the time....
so yeh, it's highly worth it....but with that you have to do some personal math.....driving style, mileage/year, install costs, mine were around 800 bux or so...., and of course your own personal preferance.....
keep in mind my car is a hotrod all the way, nearly....
If you want relatively stock, there is no reason to reinvent the wheel. Just get a TPI- easy to get components, proven, reliable. I have TPI in my 69 and also an 83 pickup. If you want to do many modifications, then aftermarket is better.