First things first. It is a mismatched rifle so I know it is nothing to write home about but the stampings made me curious to research a bit.
These are self explanatory
147= J.P. Sauer and Sohn, Suhl Germany
1939= Year of production (about half way through production run) 16.4 Million produced!
X= Russian capture?


Elaborate on these a bit if you can

and

Erfurt Rifle.. you may want to move this to the C&R forum for better traffic, and people that know more then me.

K98K forum

Info on the stamp codes from K98K forum.

Yes X is an RC.

X represents crossed rifles applied by Russians.

the small stamps are Waffenampts and are inspection stamps.  The numbers iirc are for a specific officer in a plant or region assigned as an inspector.

Like G.A.W. stamp on a Garand stock

147 is a JP Sauer und Sohn K98k receiver (Erfurt was code 27 in 1939)  

As mentioned the "X" is the Russian capture ownership stamp by then so well worn the 2 crossed rifles look more like the letter X

The only thing matching the receiver is the attached barrel. All other parts are from vast parts binds when these were all stripped and rebuilt by the Communist

Some had their Swastikas removed, peened  (Peened comes from the sound made from the metal being punched by a hammer) Others did not.
Some had the parts used to reassemble a gun electro penciled with the receiver SN and all had the receiver SN stamped on the left of the butt stock

The K98k website is a great source of such info

Same gun has a small italic letter i stamped on it. My Google-fu is weak because I can't find anything on it. Any ideas?

If you mean under the serial number that C would stand for 30,000-39999 as in these were number by lots of 10,000 so no letter is 1-9999, a is 10,000 -19999, B is 20,000-29999 and C is 30,000-39999 d,well, is you get the idea.
If they get to the end of the alphabet they double up the letters as in aa, bb etc etc
In 1943 BYF (Mauser Oberndorf) started going 100,000 per SN batch all others remained 10K batches

The Nazi Eagle was a firing proof the others were inspector proofs. If it has different numbers the part originated at one maker and was shipped to another for finishing

The head inspector kept his proof number so you will see WaA63 start out at Mauser Oberndorf then move to the Brunn (Czechoslovakia) factory as one example
There is a book dedicated to Mauser stampings for all nations, helpful to insure it is legit

It's always cute when a fake stamp is used for a gun that used to have that WaA# but should be a different number for the later year. Most forgers are smarter than that