I just checked, the Encore barrel is .990 around the scope base holes and frame. You may want to check if that White barrel has enough meat in that area.

The GM barrel blanks have plenty left to contour anyway you like or need.

You really should consider the Begara Full Contour 45/70 for a 1-20 45cal. Its about the same price ($219 or less) and already has the hanger. Another $150 for plug work and you have a fast twist 45. Slufoot even recrowns it for muzzleloading. Usually takes less than 2 weeks. These builds will even shoot a 200gr SST over 2500fps with ease if you want to quit "smoking".