OK, here's the scoop with Ashley:
There's a downloadable 20-something-page catalog in .PDF form that you need to download, the address is:
http://www.ashleyoutdoors.com/ecom/pdfcatalog.html
They stupidly named the section of the website that contains it, "Paper Catalog" so everybody misses it. It's almost 5megs in size
.
Anyways. In there, you'll see that the Big Dot and Small Dot tritiums are regular catalog items for the SP101 and GP100 fixed-sight models.
There's also a NON-cataloged front and rear setup for the GP100 that you have to call them for. That stuff would probably fit on a Super Redhawk as well.
If you can't download or read the catalog, don't sweat it, call 'em up. Contact stuff is at:
http://www.ashleyoutdoors.com/contact.html#contact
The main web page is at:
http://www.ashleyoutdoors.com - I mention this because the links I provided above are the "break out of the frames" addresses so from those, you won't be able to see the rest of the site.
What else...from the examination I did of my friend's SP101, and from how extremely low-slung the factory sight is, I personally would go with the small dot versus big dot. The big dot front might "totally overwhelm" the rear gutter channel. Remember that the center Tritium tube is identical between the two, as is glow level at low light.
I think the big dot front needs the real Express rear to work properly...not 100% sure, mind you, but...hmmm. The short barrel will put that Big Dot "right up in your face". That doesn't seem optimal.