The only .750 bore OEM chokes ever made where factory flush (which were stainless, and I have a mostly complete set), OEM chokes made for Kolar by Angleport (stainless, cannot be blued) and OEM chokes made for Kolar by Comp-N-Choke (stainless, cannot be blued).
Unless they custom cut a one-off set for you, I'm dubious.
Kolar originally made their own flush .750 bore chokes. The designation is S-55, and is the same choke they used in the 90-T (when the bore size was appropriate), and the same choke they used in aftermarket choke installations (again, when the bore size was appropriate). Wrights still uses the S-55 designation for their .750 bore kolar chokes.
I believe the window of mfg for Kolar mfg'ed flush 750 bore chokes was VERY short, since I've only ever seen a handful of guns that had them.
Then they contracted with Angleport, using the design pictured above. Some time later, they contracted with Comp-N-Choke to make a choke tube of the same design, only difference was the comp-n-choke made chokes had a little heavier knurling.
The choke pictured in this post is their most current generation of choke, I would assume also made by comp-n-choke, since I have no evidence they changed contractors again.
The new extended .740 bore titanium chokes are made by Extreme.
To my knowledge, Kolar has never produced an extended 750 bore choke in house.
You may be correct as to Hastings being the mfg of the short black extended 740 chokes. They are identical in design to the Hastings Quick Change aftermarket chokes that were made for numerous mfgs in the late 90s/early 2000s.