A second reason for moving the rear backward is that the '47 to '54 trucks have the pin in the spring forward of what should be the axle centerline. If you don't adjust for that when you change axles you'll find the axle even further forward in the fenders than the stock arrangement.
There is a kit available for this conversion that most likely would set you up for success.
One comment regarding the Nova clip versus Mustang II approach is that while fabrication skills are more important doing the clip approach, welding skills are required for most Mustang II setups also. With few exceptions those crossmembers must be welded in.
