The easiest way to find out the engine number is to look it up on the data sheet in your service/ maintenance booklet. Its the very last page. Kinda blueish and in German/English.
All important info can be found on that sheet.
Otherwise you'll have to look on the block itself and I don know where exactley the engine number would be stamped into there.
Isn't your car still under warranty? Even if not, perhaps the dealer will do a goodwill-repair. Doesn't cost to find out.
Sorry to hear you go through all that trouble.
81 300 SD grey/palomino 168K miles
84 190E 2.3 black/grey 64K miles (wrecked)
85 190E 2.3 maroon/palomino 92K miles
88 300E desert red/palomino 204k miles
(made to look like a '94-95)
92 400E desert taupe/creme beige 120K miles
(converted to 94-95 E420 looks)