Its a good starting point. However, as has been said the only thing from a performance standpoint on the "motorhome" version that's of any real use is the short block. Take that and add a good set of heads and better pistons and it can be a very respectable power maker.

Also, you only need to enlarge a 413s 4.18 bore +.70 to get to the 4.25 bore of the 426 wedge.