Hopefully this can help someone else out that has this issue, I had the error "Error 1 There was an exception running the extensions specified in the config file. ---> Maximum request length exceeded" displayed when publishing what I believed was a relatively straight forward SSRS report.
Upon googling most of the solutions tended to hint at it being related to a large mapping component being present, however this wasn't present in my report.
I then realised that the report I had written was done by copying an existing report as a starting point, that report had a few very large (file size wise) images, although I had deleted them from the report. Looking in the Report Data > Images location I can still see them referenced in there, deleting them from there resolved the issue.