So,
Thought I would pass this along. Found a thread on a random site where a guy bought one of those engine cradles on wheels, made for a SB Chevy. He bolted his 250 to it directly by using the side engine brackets from a 67-72 chevy truck that came with a 250. In other words, it seems that Chevy designed the 250 engine brackets so that they would emulate the mounting points of the SB, or the other way around. Following that logic, if you use the tubular type V-8 aftermarket crossmember and the 67-72 250 engine brackets; the 250 should mount up pretty well.
I believe that the (rubber and steel) motor mounts are the same between the six and the 8. When you look it up on RockAuto, they make references to the mounts fitting V-8's when you look up the mounts for the 4.1 six.
Larry W.