The original front sight may be to low to match anything up to. Here is an original colt spec rear. Personally I would replace both. http://www.midwayusa.com/viewproduct...tnumber=160706
The higher rear will make your POI higher but any adjustment to the front may be hard to do depending on how much is left of it.
There are several dovetail sizes but the series 70's dovetail cuts are known as Colt or GI spec. So get the set that is for GI or colt with narrow front tenon.
Like this one. Its backordered but this is the description your looking for