If I wanted to put a scope on an 03-A3 and I had one that didn't have scope I'd go buy one that already had a scope (and beat the owner down on price). I think it would cost more to convert the top to take scope mounts.
I have a 1903-A1, a 1903-A3 and a 1903-A4 with scopes. I also have a 1903-A1 and a 1903-A3 that weren't sporterized.
Before you put too much money into your rifle check it out and ascertain if it's a 2 or 4 groove barrel and the shape of the throat. If it's a 2 groove, run a borescope in it to check the quality of the rifling. Those barrels were rifled in about 2 minutes per barrel so it's easy to have chip damage. That doesn't mean the rifle won't shoot but it could affect accuracy. 4 groove barrels were made way slower to ensure quality. Check those for pitting as mercuric primers were shot in those.
It will surprise you how accurate the 1903 series are.
