i think the confusion here is mistaking a spline-cage for spline modelling...all a spline cage is is a bunch of guidelines which you draw based on your blueprint, which you then just use as a guide for ordinary poly modelling...as opposed to spline modelling (which doesnt work well at all)
tomsullivan donated a spline cage, just download the max file and have a look
http://www.smcars.net/forums/chevrol...ht=spline+cage