So you're saying a common head with cylinders that point out to two cranks; one on each side? Like a normal boxer layout from left to right would look like
Head-block-crank-block-head.
But you're talking
crank, block, head, block, crank?
I've never seen it done but it should work just fine. I think you'll have a tough time designing a head since all of your valve train, flow paths, and other goodies will have to now share the same space. You'll be doubling the requirements of everything in the same linear space... unless you're still talking 2-stroke...