Rod,
Quite honestly, I think the Malibu is kind of plain and in many cases, under powered. So I am not opposed to dressing it up a little and also boosting performance. I recently bought a 70 Malibu conv for my wife which had pwr & air, a 307, 3sp (changed to 4sp when I got it) and a 10bolt 3.08 non-posi rear. It still had the 3sp column with the shift knob on it and I changed it out with a floor shift column. Also, I added factory type cruise, replaced the 307 with a SB400, replaced the Saginaw 4sp with a Muncie, replaced the stock wide 2spoke steering wheel with the Chev optional 4spoke wheel, added a complete Cowl Induction hood system and this weekend I just installed a 12bolt 3.07 posi. When I built the 400, I installed an early Z-28 aluminum hi-rise intake and the finned aluminum valve covers and ceramic headers. When I bought the car it had fresh paint, a fresh reproduction interior and conv top and 7in Ralleys and white letters. Everything else was very original and I'm quite sure was what came on it in 1970. The most noticeable thing about the car was the new paint and wheels. Otherwise, it was mostly a stock looking Malibu. And now, the car is a completely different car because of just one change, the Cowl Induction hood I added! Just that one exterior change gave it a totally different personality. I sold the 307 and Saginaw 4sp as a unit (I don't care about matching anything except paint). With the new hood, 400, Muncie, cruise and posi, it looks good and runs super, and with the 3.07 and cruise I can go down the interstate, top down or up with cold air at 75mph in comfort. My whole point here is if YOU, not someone else, wants everything to stay original or you want to dress it up and boost performance/handling then do what YOU want. It's your car and money, make yourself happy. Did you buy the car to compare all the numbers on it or enjoy it. Some people who replace an original engine like to keep the original just in case, that's fine. The only thing I might do if I were you is to keep those early plates and ALL the paperwork. Also, you might pull the back seat (back and bottom)and look for the build sheet. If you find it, CAREFULLY smooth it out and preserve it in a plastic page sleeve (press it in a big book). I do have personalized plates on our "special" cars: 56 VETTE, 5SP-455 on the Cutlass and my wife's initials on the conv (excuse me, HER conv). Personalized plates are nice and so are early original plates.
One last thought, I do totally agree with MoeMan. It's only original once, but it's also your choice.
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[This message has been edited by DZAUTO (edited 06-04-99).]