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.
Thanks for clarifying my error on over bore. I was going on 45+ year old engine work I'd had done, plus tired brain cells.
As has been mentioned, they work good to replace 426W blocks, which were getting scarce even back then. My current 426W is a 413 block I'd bored to 426. It's certainly seen its' share of abuse over the years and hasn't failed me yet.
