Seems to around 8mm to 10mm of shims .
??? Seems way too much... ??? am thinking maybe your guards need to be reshaped up to meet the cowl. Have the guards been replaced? Some of the replacement and repro guards have to be reshaped just to get them to work.
How well do the swage lines, where the doors and fenders meet, line up? The upper swage line is the critical one. Be aware they were often not very good from new, tolerances were very wide on these old jalopies.
I've seen 'U' shaped shims recovered from dismantled cars, in galv steel. Were I to need them I'd use modern hard plastic 'U' shims as used in the building industry for installing windows etc, they come in a range of thicknesses, hidden once installed.