Saw this car the road once, and trust me pics don't do the justice, its such a looker in real.
Its like those British Rock bands of its era; ever green, hardcore, pure to its soul and a lot to say - but on the best notes: only those who've ever witnessed the aura of charm and madness associated with these type of classics can understand the worth.
To have such a classic restored in such a condition is simply a blessing in my humble opinion. Its like LED ZEPPLIN united. Now, ofcourse you can't undead Bonzo, so having a nice engine swapped is still a bargain, like Jason Bonham bashing drums, indeed.
Best of luck mate - hope you'd be keeping your Mustang for a longer time unlike this poor little fellow.