Howdy
Does it look something like this?
This one was made in 1958. Pay particular attention to the shape of the rear sight. Notice there are no 'ears' coming up off the frame to protect the rear sight. That makes this one a Flat Top, and yes it adds value.
This Three Screw 357 Magnum is not a Flat Top. Notice how the frame comes up at the rear to protect the rear sight.
And yes, just like the original Colt Single Action Army, there is no transfer bar in these guns. It is not safe to carry fully loaded with a round under the hammer. If it happens to fall on the hammer spur, it will very likely discharge. That is why in the 1970s Ruger redesigned all their single action revolvers to include a transfer bar. If you want, you can send it to Ruger and they will modify it with new parts that include a transfer bar. They will do this for free. I do not advise it, the gun will not be the same, and you will have destroyed whatever collector value it has. Just learn to keep the chamber under the hammer empty. A little tough to do because unlike a Colt the chambers are counterbored and you cannot see the rims from the side.
The way to load one of these is to load one, skip one, load four more, then without allowing the cylinder to rotate backwards, cock the hammer fully and lower it. It should be on an empty chamber. Practice this with dummy rounds or snap caps over and over again until you have it right, because you cannot see the rims from the side. Always assume it is fully loaded.
Yes, mine has the XR3 grip frame. Sorry, I can be of no help regarding after market grips, mine still has the originals on it.