The ford plow should be ok to use.I don't know about a serious accuracy flaw with a set forward axle,but why they are set back is because a set back axle can carry more weight on the front axle,plows would possibly over load a forward axle.
Try googling some western state plows because set backs aren't really for the west.
If you have an autocar kit swap frames,then you could build a forward axle autocar as well
Steel frames were probably standard.I cant see why the engine couldn't be kept turbocharged,swap autocar or freightliner parts if you don't want it.Ford and internationals have tilt hoods with small peek-a-boo butterfly openings on each side to check oil and such so a custom hood like that could be possible.
Here is a link to some brochures.The first 2 on the list will give you pics of set back dimensions, front of fender design,and butterfly hood options
http://public.fotki.com/modeltrucks25thscale/truck_brochures/diamond_reo/