413 motorhome/truck/industrial motor "chat"
I dont know anything about these motors but as far as pistons go if the ring size is available you can have what ever you want made $pecial for you.
Big RV = Small cam I wouldnt bother with the Trick of the month cam for it. Just something small.
Heads, The usual work. Valve job, clean up mill. I think this is a build were Good machine work is more important then what intake is sitting under the Plastic Fantastic.