It has been some time since I've taken out a blower...but taking out the entire shield behind the engine is something not necessary.
You have to take off the lower windshield trims, cap/panel behind the battery and unscrew the black plastic cover behind the steel shield (you mentioned). Remove the additional cover around the wiper and unscrew the air intake cover. This air intake cover can be "spooned" out fairly easy.
Then you have to remove the wiper mechanism (complete mechanism (4 bolts (I think) of which one in the shield), motor and cable to be disconnected by a plug). To take out the wipersystem, it is recommendable to take off the wiperarm (makes shoving the complete system easier).

Like I said it has been some time since I last took out the blower, but this should be about the things to remove before you see anything of the heater system and blower housing.
I can not help you with the part# necessary.

greetingz & good luck,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)