The grip frames for the BH's were aluminum for many years. The newer medium framed model have used steel.
As for swapping...yup, simple swap. have done a number of swaps. If using an unfitted, in-the-white one though, you'll need to get a new trigger spring retaining pin and grip locator pin and install them as well. MUCH easier than trying to remove and reinstall.
There are differences however. Ear height has changed so an exact fit there isn't guaranteed. the alignment stud has been removed from grip frames and the aligning void in the cylinder frame has been eliminated so having one and not the other can require additional fitting.
Now if you're after brass, you're limited greatly. They're out there but now commanding rather high prices. be sure you're getting one that fits your gun too. (OM/NM stuff) last aftermarket one I saw sold for $300+/- and genuine Ruger mad ones a bit more than that. The birdshead styles will be up there and the VERY elusive Bisleys ones will be even more still.