I don't know about the .45ACP Rugers shooting low rumor, but my New Vaquero and Vaquero (two in the center below) chambered in .45 Colt shot low.
The good thing is it's a relatively easy fix (especially in stainless). Establish what load will be your "go to", then head to the range with that, your Ruger, and a file. At the range, determine at what distance you want to regulate your sights, then,
carefully (
while checking the results repeatedly), file the front sight down until your groups are up where you want them.
Here's the target I used while doing this with my New Vaquero:
As to .357Magnum magazines. ProMag did make one for the Desert Eagle. It's been discontinued, but when they turn up on auction sights they are generally cheaper (mid $20s) than the Magnum Research versions.
I wonder if a .30 carbine magazine would work?
Regards,
Greg