I put an aftermarket blocked Hemi in a 68 Dart. The outside dimensions of the new blocks will have differences from the originals. In the end, the ONLY way that I got it to fit was to buy an engine mount kit for the 'K', set the engine in and then tack the mounts together with everything in place. Then I removed the 'K', fully welded the mounts up and had it powder coated. Otherwise, a fraction of an inch or degree of measurement off anywhere meant it would not work. There is NO room for error.

Just my experience.