Yes it can be done but don't expect to get straight into the rhs of a 747. Your hours will be factored by the airlines but the fact that they are multi-crew, multi- engine will help, any single pilot hours do not count for much with some employers. You will need to get a CPL(A) then get some hours flying something commercial. You can however use some of your helicopter hours towards the ATPL. Most airlines at the moment are looking for hours in something above 25tonnes but there are exceptions and jobs are available for someone with your experience. Best of luck.