Old colt lower/new AA 6.5 Grendel upper

[Variable]

Does anyone know if Alexander Arms offer their current 6.5 Grendel upper being able to mount on the old large pin/small pin Colt lower

More info needed.... Do you mean you have a large front takedown pinned Colt lower (SP1 and similar)?

If so:

http://blackrifleworks.com/colt-ar-15-un...p-164.html

Or

http://shop.ar15sport.ihoststores.com/pr...T-CLT-ADAP

Or

http://www.brownells.com/.aspx/pid=24948...ER-ADAPTER

There are likely also others. What is the diameter of your front takedown pin? Is it .315 inch?