Fast forward- 5 years from now where do you see the value of your Mustang vs the value of the Viper? Historically speaking, I'll venture a guess that your Ford will appreciate while the Viper may or may not. As long as you see yourself still ahead of the game at some point down the road when the Viper is on the block, I'd say it's definitely worth considering. If not, it's like trading coins for magic beans, right? Don't forget about insurance rates and reg fees- I'm guessing they'll be considerably higher ( at least they would be here). Just my opinion, but I'll pass every Viper/Vette/VW at a show to get to the older Ford stuff.... of course I haven't driven one either... Damn- good luck with that brother!
Working on old cars teaches us patience... and every curse word imaginable!