Your road noise intrusion is very likely from an open hole somewhere in the firewall. A single 'direct path' can ruin a lot of well thought out soundproofing.

Nice job so far...Id like to do the same thing someday to my 123...

__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car