Well, thanks again for all your comments! Allow me to answer back to some of your comments and tell you a bit about the car and myself.
When I decided to finally get a Firebird it was because I thought it was simply beautiful, and just as old as me.So after some years I found one, went for it, and flew up to Finland 2500 miles away north from Luxembourg... and drove it back down. And there it is, right in my garage.
Finally I lifted he hood and started looking inside this 50 year old purely mechanical gathering of turning and spinning parts. So, what did I have inside there and mainly what did I have in front of me? The understanding of it was not just obvious. Internet started answering my questions. Frame , parts mixed up with the ones of the camaro's, same or slightly different GM engines as in plenty of other car models and brands... and more confusing info to me.
Fantastic, just like a treasure hunt to figure out what I have, what is original, and what was swapped, changed or repaired in the last 50 years.
And obviously as expected I've posted you some of my noob wrong conclusions . Seems that I don't have a Chevy engine but a Pontiac engine... I thought the 350 where the same in both cars... I probably will still surprise you experts with some more "funny" conclusions :-)
More to know is that I got my hands on the history of the car since it came over to Europe. I was imported form US to Finland and had something like 17 owners before. Who knows what has really been done to it. The general state is excellent. Some body parts have been changed and globally it is 95% rust free. Many little details can be fixed with aftermarket parts. I already placed a big order on classicindustries.com to fix the aesthetics, inside end outside.
Concerning the engine I still don't know what have in my hands and how much it is running "wrongly". I have big troubles finding the engine numbers. Could they be simply not accessible? The only numbers I've found were some 4 digit numbers on the sides where the manifold connects to the engine. Are those indicating something? Consumption is over the acceptable limits. It has a leak at the back of the drive shaft and leaks a bit oil under the engine (not yet checked from where exactly). It came with a brand new carburetor, and 4 new shocks. I guess that the previous owner had already a guess on where the consumption issue came from... Finding parts and advice in Europe is very difficult so I must make sure I know what the issues are in order to order the right parts from the US.
My business is selling racing off-road bikes since 15 years and I have a well equipped workshop. I am not a great mechanic, but I know how to use my hands.
This is my introduction to you folks. I need and will appreciate extremely much your advice. Thanks for reading me and for your patience, since as I said I am a noob and my questions will probably make you often have a funny day :-)