There is a TBAS on Ebay for what seems reasonable, He also has a gator 6 jaw for sale, I already own a TBAS with a Gator 6 jaw or I would probably get this myself. Don't know this person, Just stumbled across this listing when looking at chamber reamers. You would have around $3200.00 in a TBAS and 6 jaw if bought new.
It is for a D1-4 spindle.
I posted this here to help out fellow smiths.
It is for a D1-4 spindle.
I posted this here to help out fellow smiths.

STRAIGHT SHOT GUNSMITHING TRUE BORE ALIGNMENT SYSTEM V3 / D1-4 | eBay
IT DOES NOT INCLUDE A CHUCK, MOST 6 1/4" CHUCKS WILL WORK WITH THIS UNIT. THE BACKING PLATE IS FOR A D1-4 SPINDLE. ACTUAL ITEM IS DISPLAYED IN PHOTOS, WHAT YOU SEE IS WHAT YOU GET.
www.ebay.com