Chassis ID - is it an M375 or M400?

[Real Wrought]

Chassis Identification:  Simply identifying this dodge motorhome chassis seems unusually complex.  The VIN calls it an M400 chassis but I read somewhere in this forum that since I have 17" wheels with a 5x8 bolt circle it's really an M375.  I've also seen "M300/M400/M375" and also "RM350 or RM400".  Question - Has anyone ever really cracked this nut and described it clearly anywhere?  Where is that summarized?

I have the original Dodge 413-1 V8 which I believe is called a "Max Wedge" engine.