parts interchange from a 71 to a 69 blazer

[buckshot]

i bought a 71 jimmy for parts but it has a better body than my 69 so,i thought i might do a body switch between the two.i've noticed a couple of differences in them.one is inner heater/air box the 69 has a metal one and the 71 is plastic.can the metal one be used in place of the plastic one?the second thing i noticed is the accelerator pedals are different-can i use the 69 type in the 71?sould i even worry about the differences.no one outside this board,or wes's would probably be able to tell the difference.any help will be appreciated.