That's as maybe now, but, as discussed upthread, doubt that 1960s/1970s era BR would have wanted a heritage railway outfit to have access to their rails, and, if successful, show up the BR management who had withdrawn the Whitby -> Pickering -> Malton service.
Also, hadn't the six miles of track from Pickering to Rillington Junction been lifted with the usual undue haste by c. 1966 already? Don't think the NYMR was founded until the following year and it then took them some time to get established.