Magnum 300 crate engine - how should it go when tuned up right?

Well done, man.
I need to chew on the info a bit but your points about the ratios are spot on. That definitely makes sense and it’s making me wish I had the budget/time for the T56 swap already.

So this may be obvious to everyone but me but aside from the governor weight, what Needs to be done to hold off that shift for 400 more rpm? Aside from the Dart, I drive nothing but manuals...I always thought the biggest benefit for the slush pump was that you set it and forget it. :D

Well, traction isn’t that big of an impediment so far. Launching around 2500, it burns the tires for ~15 feet and hooks...I tried rolling into the throttle less abruptly to spin less and the times were significantly slower. So...compression test may be necessary? The motor doesn’t smoke so I’m hoping that the tuning may be more relevant.

Yeah the Mustang is a 3600lb landwhale but it has a motor that pulls from 2k straight through 7300, 285 wide W-rated tires and six gears. It’s not a fair fight. I opted for the 3.55s over the 3.73s because it would trap in 3rd rather than 4th. Someday, it’ll make it to the drag strip. Lol Trust me, if Dodge offered a sub 4000lb muscle car that was smaller than a Country Squire I would have bought it.
There's a reason ,why you paid that price tag ,on that Mustang..GTX..
Just keep that in mind, and old school works .....and be patient....