For anyone interested - I managed to get it working reasonable well using a hybrid of Knap's 3-4-3-0, Pandemo and my own front 3 flavouring
I have Iheanacho as a RMDa on the right hand side, Vardy at the central forward position (offset to the left to open more space for iheanacho) and I have brought in Perotti from Roma to play a playmaking inside forward support role to distribute to the two finishers. Gray is now coming off the bench and training as a AML advanced playmaker in an effort to see him develop as a future perotti - failure to do so will see him sold as at the moment his pace and dribbling does not have an end product (passing/vision/finishing/long shots all <11)
Working exceptionally well for the set of players at my disposal (better than the top plug and plays were) due to the perfect fit of players in different roles to the 3 AMC that most plug and plays use now.
Biggest lesson learnt from this is it is really really important to modify tactics to your own players strengths and to correctly distribute the playmaking and spacing of your players as overloading the AMC slot will not work if you do not have skillfull high balance high passing players to create a through ball chance - running 3 poachers in the AMC slot playing SSa does not work - your far better off with 3 APs in those SSa slots as they will find the pass to unlock the defense.