66: Do what it takes to make it enjoyable to drive on a sunny day without the little issues (whatever they may be) annoying you. This way you always have access to a fun car when the weather is nice and you're not stuck forever in project status with at least one of them.
67 GTA: let this be the long term project. Make it what you want, and take the time to do it right. You have your 66 to keep you motivated in the mean time. (side note: if you're not hugely motivated by sentimentality of it being your dad's car, and it seems like you aren't, consider selling it to finance a plane jane, non-S code 67 fastback build. S-codes are rare and expensive, and it could do a lot to finance your un-reversable mods like minitubs. Or not, whichever)
Eleanor Project: Tell your close family friend to pound sand. Eleanor is a played-out whore of a car and can't hold a candle to a 67 S-Code fastback. The thought of selling one (and a solid 66 coupe) to finance an Eleanor build makes me want to punch a baby.
How's that for an opinion? lol
The anvil of reality.