Ron Hoehn has Shilen 12 twist lv and hv barrels in stock. If someone wants a Grinch he also has a reamer and bullet seater. Resizing dies on the way. Billy Stevens also has a Grinch reamer.
The Grinch holds 2 grains more powder than the grendal so the loads will be different but I think LT 32 and 133 are both to hot. I think your on the right track with the 8208 xbr. It shoots well in the Grinch also. If you check velocity with the 80 gr dominator it does best between 3120 to 3220.
Pablo,
You might want to go to 6MMAR as a starting point, thinking this will give you multiple starting points, with the advantage of going hotter for the bolt gun. But gives you listing of powders that work in the necked down 6.5 case.
Hope this is helpful.
http://www.6mmar.com/6mmAR_Turbo_40_Improved.php