Lol, Toyota merely THREATNED a lawsuit, there was never one filed therefore you will not find any written "proof". Lincoln changed the name from LS6 to LS V6 under the condition toyota changed the T150 to Tundra.. Saving both maufaturers from a lawsuit and thus being swept under the rug.
The name is supposed to be evocative but has no grand meaning. Pontiac chose it because it likes the letter G — GTO, GTP, Grand Prix, Grand This, Grand That, Grand The Other. And 6, besides suggesting a mid-range car (on a scale of 10, anyway) is a number that legally could be used with G without inviting a lawsuit from owners of other G-series alphanumeric nomenclature.
For instance, Lexus uses letters to indicate relative size and numbers to denote the engine size in liters. Think of the ES 330 as the "executive sedan" with a 3.3-liter engine and the LS 430 as the "luxury sedan" with a 4.3-liter. The carmaker borrowed from gran turismo (the original long-distance auto races, not the video games) to come up with its gran sedan (GS).An international sedan (IS)-not coincidentally, a big seller in Europe-and a sport coupe (SC) complete the passenger car lineup. The SUVs follow a similar pattern. The RX signals a "recreational crossover" and LX, "luxury crossover."
BMW and Mercedes have used similar grammar for years. For BMW, the first digit represents the class-3, 5, 6 or 7 Series, in increasing order of size. The German carmaker reserves odd-numbered series for sedans and even-numbered ones for coupes. The last two digits indicate the engine size in deciliters-or, at least, they usually do. In just one example of understatement, the BMW 325i has a 3-liter engine, not a 2.5-liter as its designation would imply. Letters at the end denote other specifics-i for injection (a vestige of the era when you needed to distinguish between carburetors and new-fangled fuel injectors), x for all-wheel drive, C for coupe, L for long wheelbase, to name a few.
For another thing, carmakers encounter fewer trademark infringement problems with letters and numbers than they do with names. That didn't stop Nissan's upscale Infiniti brand from filing a lawsuit against Audi over use of the letter Q to designate a line of SUVs recently. But on the whole BMW doesn't care that Mazda also has models known as 3 and 5.
I hope that helps to answer your questions...
I used to call my friend's turbocharged IS300 that. 
