I apologize if I sound harsh but I would sell them all.
They are all mediocre vehicles at best, although the T-bird is mildly interesting.........if it's all there, but it sounds like it's not. Pro tour the T-bird possibly?
The mustang needs to go right now. The 300M is downright boring so it needs to go.
As for your truck, that would be your call. From what I understand, you have a lot of money tied up in it. You'll never recoup it all if you sold it. I will say this though, the money you spent on your GMT400 truck, could have gone a lot further on a Dodge Cummins truck (yes I said it). But that's nether here nor there. Despite how much was spent on your truck, it is very unique. It might be worth keeping just for that reason.
My thinking:
Sell them all except for the wife's daily driver.
Buy a 100,000 mile Dodge Cummins (2006ish) crew with 8ft box.
Then buy something interesting like maybe a 2006 GTO.
Both above vehicles, with a few mods, will up your fun factor by 100%.
Hell, in stock form they will do that.
Just my opinion.
No offence taken.
Allow me to rebutt:
I wouldn't mind a Cummins, just not interested in the dodge they come wrapped in. I've got a couple friends with 'em and they are capable trucks, but it feels like I'm riding in a "cartoon truck" everytime I'm in them. Nice features, comfortable and powerful but not for me. I'd get a 7.3 power stroke before a dodge.
I spent the money on the truck because at the time I had no choice. We were on a cross continent move, the engine popped and I was in the states. Financing a vehicle out of country wasn't an option and I didn't have 20-30,000 in liquid cash. Dropping in a new engine was about the only viable option. Turned out to be 10,000 (with labour) so I'm stuck with it for several more years until I at least get some use out of it. If someone offered even trade on an eclb duramax or Cummins dodge it would be gone before I could get the keys into their hands. But that's pretty unlikely to happen....
The bird is a cruiser, a stronb runner as is and complete. Im also a big tbird fan ( have had many of them). Problem is the rust is extensive and requires major work to make it road worthy to my standards. I mean MAJOR work. I could slap it together, but thats just not me. So its going to be stupid amounts of work and money to finish it. Not sure I want to go there. So far there's only 2 grand into it and I could get that back out of it easily.
2006 GTO? My turn to be harsh (no offence intended): gross. Completely and utterly gross. Other than the drivetrain, boring as hell. Might as well put the corvette underpinnings and drivetrain under the M. At least that would be fast
and interesting. GTO: No thank you.
Mustang is what it is. I like 'em, you don't. That's just personal prefs. No harm no foul. That would likely be the easiest and cheapest build if all I wanted was speed though.
The M is a car that has to driven to be appreciated. Its no 1/4 monster, its no autocross hero, and its not the most visually stunning car (about the same as the 06 gto there). But its good enough at all that to satisfy me and I could jump in it right now and cross the continent in comfort and safety. Problem is: if it becomes the "project car" all that is likely to be ruined.
Like of thinking to do before I do anything....