We spent an incredibly frustrating 1.5 days changing the front number plate on the e21 over the weekend. I actually went to fix a rattle in the front driver's side strut. That took all of 5 seconds (it was a loose nut on top), so I thought I'd put on the new Historic Plates. Turns out the old plates were pop-riveted on to the fibreglass Alpina bumper/spoiler. We drilled those out and figured we'd just put some small bolts through. First problem - new plates are smaller and there is an ugly section where the old plates were. Easy - we'll attach a piece of aluminium to the bumper then the plate to the aluminium. Next problem - there was no way to get my hand behind the bumper to put the nuts on. This was obviously why the old ones were riveted. Next solution - loosen the bumper to allow hand in there to do the bolts up. No good - The grill is in the way so it won't rotate far enough. So ti was time to take the grills off. Once the grills were off, I took the bumper off completely as it was already disconnected. The actual attaching of the plate was about 10 minutes. Then we could start re-attaching things. The bumper was a bit of a pain. It wouldn't line up properly and the attaching screws were embarrassing - most were wood screws! Finally got the bumper in about the right spot just in time to tidy up as it was getting dark.
Got back into re-assembly next morning. I decided to use some better grills and blinkers off the wreck out the back as the old ones were all cracked and the attachment points broken. They looked good after a tidy up. The next problem was that the driver's side blinker wouldn't line up. It turned out to be the grill not lining up as the blinker is mounted through the grill - thank you BMW :( . This was because the headlights were in the wrong spot, forcing the grill towards the centre of the car. Some inspection showed that there had obviously been an accident at some point and the front of the car was badly repaired. I knew this when I bought it, but had no idea it was this bad.
The light mount was still pushed in about 10 mm. So we took the headlight assembly out and fixed it as best we could, then elongated the mounting holes to get it in the right spot. Now the grill fitted nicely. The other grill was less of the same and we managed to get it in with less swearing. I also took the chance to fix the broken passenger side blinker while I was there. Finally got the centre (kidney) grill on again and added all the missing screws that the dodgy repairer hadn't bothered with. Also put some grill clips from the later e21 just to be sure. Gave her a wash and she looks exactly the same! Luckily, I know how much better it is underneath.