A dedicated bus-train interchange service was attempted by LCC and MPTE in 1979. Operated by Ribble and numbered 395/396, it operated between Skem (and its environs) and Kirkby station, connecting with the Merseyrail service to Liverpool Central. It took exactly an hour between Skem bus station and Liverpool Central (roughly a five-minute interchange at Kirkby). I don't know if through-ticketing was available - doubtful?
Whilst the service was well-intentioned, it was deemed a failure because it didn't really save much time against the 305/345 through-bus service between Skem and Liverpool (one of them operated through Kirkby too). Perhaps the 395/396 services' legacy is that's where the seed of MPTE's aspirations to reach Skem by Merseyrail came from?
I would like to see the Skem extension happen in the next ten years - the Headbolt Lane extension is a small, yet significant, step for the project. Unfortunately, there's two disparate authorities (LCR and West Lancs) and an unsympathetic central government involved - it will take a miracle to get the funding. If Skem had been included in the metropolitan county of Merseyside, as originally envisaged (Southport got the nod instead), the rail link would probably have been created by now.