On the P-47 Republic used 89 followed by a letter followed by five digits and then often followed by a dash and two digits.
It is unlikely they used a different part numbering system on earlier aircraft.
The R may stand for Ryan (I have never worked on one so have no idea of their part numbering or cast in markings) or it may be the casting contractors symbol. Many companies used parts supplied from Alcoa and those have ALCOA cast in. Have a look for any inspection stamps - typically they are about 5/16 high. Some of those parts will probably have been heat treated and the usual, but not the only, heat treat stamp is a circle with an H and a T inside it. Some, but not that many, parts will have a military acceptance stamp on them which will be AC, AF or AN for AF aircraft and ?? or AN for Navy (I am having a senior moment and cannot remember what the other Navy stamp was tho I suspect it was BA yet that just feels wrong for some reason). Any other stamp will be the airframe manufacturers stamp. I cannot see any stamps in any of the photos you supplies so far but that may just be photo angles and dpi.