Hey Patrik, dont worry if its proper. Do what you like
It will look cool with either muffler. If it was my car I would keep the nicer glasspack and paint it white. Then I would cut the flange and tube off the other glasspack, weld it to a quietpack, and paint that hi-temp black.
This car will make a beautiful pre-cal. The 356 wheels are a perfect choice. I prefer 185/70 or 195/65 over the big 205/65. Have fun and send me some pics when you've made progress.
So, I just looked at your pic again and one muffler has a 3-bolt flange. I would not cut the chrome, 4-bolt since it probably "original". Get a cheap quietpack, cut flange off and make your own. It shouldn't be too difficult.