sounds far in value, the Cobra is a great amp, but their resale is poor compared to new. That's not a recent trend either, it's been that way for at least the last 5 years. A rev F recto is one of the sought after revisions, so +$300 sounds like a decent deal to me. I don't think you would be losing out even if you turned around and flipped it. Adding in the +$300 on top, I think you would be getting the better end if you had to sell it.
I wouldn't do it unless you actually liked your 2ch TRec though. The differences are going to be subtle, and it's still going to sound like a Recto.