66 Valiant 6 to V8

Nice lookin' car! Since it's a slant, you've most likely got a 7.25 rear end in it- it'll work for a bit, but I'd add an 8.25/8.75 rear to the long term shopping list. And bigger (or disc) front brakes, since you most likely have the little 9" drums- with more power, you need to stop... and other odds & ends, which you will find out about. Don't you just love how these projects start to snowball? :)
Do your research, and as you read through the threads, make notes on what will be necessary, and prioritize it. Check in with us with questions on the particulars, so you only have to buy things once and end up with the correct parts. Saves on the downtime and the frustration factor. There's lots of unique parts and quirks to the early A bodies, but they can be fun little cars. You're far from the first one to travel down this road. Enjoy!