Differences between 300SD and 450SEL???

[PanzerSD]

I may be buying a 1980 450SEL in IMMACULATE shape except for some MAJOR mechanical problems, the first, being it's a GASOLINE ENGINE!

so I was wondering what all is different between the two besides the obvious drivetrain....

Questions:
1. Is the front subframe the same in the 450 as the 300?
2. will any of the A/C or HVAC stuff need to be changed?

I can do electrical and everything else, it's just the ENGINE spacific stuff I need to know about....thanks in advance...