Calculate Production Start dates/End Dates

I'm hoping someone can point me in the right direction

I have built external to Nav a production order scheduling board to manipulate production orders. Where companies use routings this is very straight forward however this particular company do not use routings and cannot due to some custom code relating to outputs.

So they have two types of machine, each has a different speed. Any product can be made on either machine.

My idea so far is to create different work centre's and different machines. Create two routing versions 1 & 2 corresponding to the separate work centres (machines assigned to each work centre) but not assigning the item to a given route within the item card.

If possible I would like to trigger the production order refresh as if production order routing lines had been created.

Externally they assign an order to a machine, this dictates the route and subsequent speed and I would like to trigger the Navision calculations for the production order durations (start date, end date etc).

Am I clear? Any help greatly appreciated.