I will start by replying to the black powder. If you choose to shoot black powder, you will be better off using the Accurate Molds 43-215C designed by John Kort. This has a large lube groove for better shooting results.
If your barrel slugged .427", yes, use .428" soft alloy with black powder....Swiss has been my preferred choice for accuracy loads.
The 44-40 "M" die should work fine with the .428" bullets, any larger and you need a 44 mag "plunger".
Starline cases are thicker than Winchester and thinner than Remington, best all around case and is my preference.
I do not prefer the 43-215C because of the crimp groove, I would rather give a LCF or Redding Profile Crimp instead. As long as you have good neck retention, a good "squeeze" crimp like the Lee FCD or the Redding Profile Crimp is more desirable. There are plenty of designs at Accurate Molds for the 44-40 bullets, both crimp groove and no crimp groove. The softer lead will allow a nice crimp.
The Lee FCD, use caution with this on larger diameter bullets. The collet with not close all the way on larger bullets and the case mouth will be forced out in between the collet splits and damage the case. Also, a too harsh of a squeeze will leave a "ring" around the case mouth. Can weaken the case when using full loads but other than that, should be fine.
Here is a link that might help.
https://sites.google.com/view/44winchester/handloading