I found a sight with windowed tunning spark plugs for youre engines... but somethings a little hanky.

Supposedly you can see the flame front color. The flame color deterimines tune or A/F ratio.

exerpt:

"ColorTune is a test spark plug with a high-temperature glass window in the center which actually allows you to look into the engine as it is running and analyze the combustion flame for color and other appearances. Since different air/fuel mixtures burn with different colors you can quickly tell if your engine in running rich (yellow flame) or lean (white flame). A correct 14.7:1 air to fuel ratio burns with a blue flame"

is this feasible?

Those have been around for decades. I used one on multi cylinder motorcycle engines in the early 80s. They worked then, but only at idle because unless you have a dyno, checking the color at speed could be dangerous. I'm not sure if the modern clean burn gasoline would be as easy to see the colors change.

I would save up more money and get something with data logging or a dynamic display so you can check the mix under load where it's most important.

I'm waiting for the rivers to start putting a full set of those in their cars for the show like they do with the LED's in the alternators and stuff.