I just sold (last friday! ) on ebay the complete front end for a Air suspension !!!for $10.
the front axle assembly is identical from W110 to W109.Same parts were used throughout.(different brakes of course)
OK ,so much for that,the main difference is the bottom A arm,it is "upside down" on the Air suspension front end,because the lower part of the air bag sits in it,the upper part is the same as the steel spring ,in fact any steel spring front crossmember has the 3 holes to secure the airbag in place!.
Converting a air front end to steel springs is a easy swapping over the bottom arm and fitting coils and vice versa.
There are two types of bottom arms for 109's though,the early ones and the later reinforced ones with a strut to prevent cracking.Always inspect potential purchases of arms for signs of cracking on the outside (kingpin) end,they fail as you pull up to a stop ,never at speed luckily.[:)]
Is your 108 a V8?, Iam selling a complete Air pump set up on Ebay at the moment.It will fit all merc V8s (except M100) up to the W126 m116 with mods.
The merc compressor will handle any lowering or raising easily with plenty of volume.http://cgi.ebay.com.au/ws/eBayISAPI....MESE%3AIT&rd=1