[Crex]

If you make the side plates part of the rail it will make a tremendous difference. Grind and shape the edges so that they fit snug/flush to the web of the rail. Clamp then drill two holes completely through for bolts so you can mechanically snug up the fit. Cleaner and tighter the fit the better. Try it out, if it suits your needs for mass and sound, leave the bolts in and weld the edges permanent.
Note: If you find getting the plates flush just a little too difficult, still do the drill and bolt up. Weld a thin piece of metal over one end of the opening, melt up a bunch of tire weights and pour into the void until full. Not quite as good as a flush fit but will still give you lower sound levels and more mass.
More under-hammer mass is very helpful when welding up layered steels. It's not so much how hard you hit but how much "mash" you get at the weld at the right temp.

On dings and hammer marks - learn to use your hammer(s). Most of us bladesmiths have more than just several hammers with many different faces, weights and sizes. Sure a lot of them don't get used much but each has a purpose. Use flatter faces for the more finished steps and learn to hit evenly and flat.
With serious practice you will likely find you don't even need a "Flatter" hammer. Eventually you will gravitate toward one or two hammers that really work for you and you will find the others gathering dust and rust.
***Don't let just anyone else use those particular hammers - you will regret it!***

Mostly it boils down to serious practice with attention to detail.