Chaz 58, I've seen several of our stepvans modified to accomodate a V8, most commonly the 350. However, any engine mod you make will require redoing your doghouse, as Bill mentioned. Guess that's why they originally used the updraft carb. Mine is a '55, but they are probably the same dimensions.
Good luck!
~ Victor
1941 3/4-Ton Pickup (in process). Read about it
in the DITY Gallery1955 Grumman Kurbside "Doughboy" 235/3 on tree w/ OD
1957 3100 - moved on
1959 C4500 Short Bus "Magic Bus" - moved on
1959 G3800 1 Ton Dually "Chief" - moved on
1958 C4400 Viking "Thor" ~
moved on to fellow Bolter 
