Feel free to drop me a PM about Cambridge if you wish, or I can answer any briefer enquiries on here. History is my thang and I went through the whole process only a few short months ago.
At Cambridge in general they look less at your GCSEs because you have to submit all AS/A2 module results to them, in turn the focus is put away from GCSEs. There's some minor importance, but this can be minimised if you're really worried by applying post-A2s, although that may be a bit extreme and only necessary if your results are poor. Most people who have this complaint are just worried because they don't have 11 A*s, and really you don't need any A*s. GCSEs are useful for candidates with poor AS results who want to show they do have potential - likewise this is reversed, and poor GCSEs -> good ASs is much better than the former.
Largely it's not a concern and my GCSEs were disappointing too due to lack of work, but it won't affect your process (unless god awful, and even then you're likely to have a decent reason). Cambridge are naturally more open as I said in my first post due to them interviewing more (I believe for history it's around 90% interview rate, and 30-40% at Oxford due to their application of the HAT, although that could be argued as a substitute to GCSEs, although often that's not the case).
Hope this all helps, PM me or reply whatever floats your boat, and if you want me to go through the reasons why Cambridge > Oxford for History defo send me a PM :P