It would be nice to know if the OP knows whether Grand dad's 03 had a receiver sight or not? Would be a big help identifying which 1903 rifle to buy.
If the OP is interested, I do have a very good article on the 1903A3 that I could copy and send him. Just send me a PM with contact info and I'll mail it off. Lots of good pictured in the article and it does show the various versrions of the 1903 and varients.
COMPROMISE IS NOT AN OPTION!