You need to contact
Mark N. Ambrose
Director of Sales & Marketing
Arrow Precision, LLC
2750 W Gordon Street
Allentown, PA 18104
813-766-7311 Cell
610-437-7138 Office
610-437-7139 Fax
mark.ambrose@arrow-precision.com
He'll have most anything available you could need
Best bet for barrels is get one for a Raptor and have it trimmed to fit,threads are basically the same.Other than that there's not much by way of upgrades needed.
Some Sterlings don't have a serial number,Mine didn't.
I'm pretty sure left feed is uncommon.Not sure price wise what left feeds go for but,the 2 right feed ones I had, I paid $220 for the first (Had a match anno'd raincover) and $150 I believe for the second