The Super RH wasn't "made for the .454." It was made for .44 Magnum and it wasn't until years of .44 Magnum production that they added .454 and .480.
The barrel doesn't "change in the middle." The barrel is a bull barrel full length. What is different is that the front of the frame extends out further along the barrel. This wasn't done for strength so much as an extended base for optics. The original Redhawk couldn't accept scope rings. Later they added them but had to put them on the barrel. Which works but you end up with a scope that is quite far out there. I've got a 2x Leupold on my SRH and it is easy to see right there on the frame.
True, the triggers and springs are different. So statistically the SRH's have better triggers. And they are easier to gunsmith to a better pull if you buy one that is lacking in that area. With the Redhawk, an aftermarket spring is about the only safe option, if that doesn't get you where you want to go, you just live with it. Otherwise you may end up with a hammer that doesn't reliably detonate magnum primers in DA.
The grip is where the differences are really stark. When I bought my first Redhawk (5.5" ss .41 Magnum) I actually liked the feel of the stock grips. Dry fired it a bunch and loved it. Finally got out to the range and put some rounds on target. First six, looked good. Even the second six. Then I was starting to shake my hand a bit and saying, "crap, that hurts." I look down and the back of my thumb is bleeding. That exposed hump will eat you up over time. But if you put on proper grips that cover it up and give you more hand grip... they become too big to be comfortable. The Nill wood grips from Germany are the best I've found for mine but they really are a bit too big for quick sight access. I have to slightly adjust my grip before firing. They are pretty and help a lot with recoil.
But the SRH doesn't have that very large grip frame. It has the stud sticking down like the GP100. Same size. So there are thousands of grips out there you can try on your SRH. From tiny little things that would look quite odd to big giant ones if you have XXL hands. You could fit a block of wood to that stud and cut a custom set in any odd configuration you wanted to try.
IMO, the SRH is a bit ugly. Or at least homely. But sometimes you want real utility over looks. Scope mounting, SRH. Trigger, SRH. Grip, SRH. For a deer stand revolver, SRH every time. Now if you want to put it in a belt holster and carry it all around with you... then you have the Redhawk. I love mine in .41 Magnum but it is a totally different gun than my scoped 9.5" SRH.
There was no 8 inch M29. That's 8 3/8th inch.
And the 29 isn't a blued version of the 629. The pre-29 was introduced in JAN 1956. They started stamping M29 on them in 1958. The M629 wasn't even introduced until 1979. So 24 years later. The 629 is a stainless version of the M29, not the other way around.
Finally, there are some newer versions of the Redhawk that are interesting. 4.2" barrel in .44 Mag and .45 Colt.
http://gunblast.com/Ruger-Redhawk45.htm
A 2.75" version with a round butt. (That fixes some of the grip problem since then you have a smaller grip frame.)
http://gunblast.com/Ruger-RedhawkTALO.htm
And now they are making the 4.2" version in .41 Magnum And a round butt 4.2" version that shoots .45 ACP and .45 Colt. Full moon clips for the .45 ACP. Interesting gun. I may have to buy the .41 Mag version.
http://gunblast.com/Ruger-RH45ACP.htm
Gregg