long block equals heads/cams etc installed, short block is just the block with crank/pistons/rods. Long block would be easier to install because you just put yuor valve covers on, intake manifold, hook up electrics etc whereas short block you have to put the heads on, set the timing, etc etc. And your rigth about the axiom motor that swaps right in being virtually identical to the VX's. The 250hp version was direct injection and is not a direct swap.