I have just purchased a fantastic 1973 280CE, W114, the 2.8 model. I have been searching the web for a complete workshop manual (Hayes etc) which will cover the entire car.
Unfortunately there is no " Haynes" for your model. Official workshop manuals are available from MB. Bootleg copies are also available on Ebay from time to time. To see what you get for your money see this online copy of the MB manual. MB.BOLINKO.ORG - /8-dokumentacja
There is a Haynes manual , as i have one for this model of car, it shares info with thw 280 sl pagoda too, i will post up the isbn number when i find it.
Autobooks will have a book that covers the 114 series but not that particular engine (which is the M110). You should be able to get the official workshop manual for it on CD.