No you cannot go the other way without cutting and welding the K-member. The problem is the V8 k-member has a raise stand on the right. The slant has a short stand, The make a bracket to raise the slant 6 stand for the V8 but I don't know how you would lower the V8 stand without cutting it off. I have a slant K-member out of a 72 slant 6 for $50 here in Pa.You can drive for it. You can put it in or cut the stand from it and have it welded to yours without removing the k-member. Either way it would be your only route.
I have brackets to go from slant to V8 from schumacher