Yes I would keep both for the summer at least. I rarely keep cars very long. The TRX would be a more practical choice to keep while still giving me some great performance.
Not sure what area to post this in but this looked like a good place to start. Are there any dealers offering below MSRP or below invoice pricing on ordered GT500s? I just ordered a TRX for below invoice and would be interested in a new GT500 below invoice. Thanks!
Definitely not inappropriate. In fact, so as to get more attention, I would start your own thread discussing this.
With that being said you will definitely be paying more for a Coyote swap than for a regular engine as long as it was done right. Unfortunately I can't really give you a ballpark...