You have a very late war 6.5 caliber M38TS. RA is just the letter block serial number prefix FNA used during this period. It was followed by the RB serial number letter prefix.
Some of the last TS made were not issued, and this could very well be one of them. I suspect it barely avoided being converted to 8mm by post-war speculators.
After the Italian king surrendered to the Allies in 1943, there was no sense of urgency in the various arsenals to apply some of the markings ( like the Fascist date in Roman numerals) so they were simply omitted.
Most of the marks you describe are armorer's marks or inspector's stamps. The "CA" bolt was probably laying around in a parts bin & was used when it was near the top. It was made earlier in the war.
This model takes the standard long rifle bayonet, and a web sling is correct.
Welcome to the site!!
SW