Revenue Recognition Changes from old system to Nav

Hello. [:D] I would like to know how you have handled these types of situations in the past. I am converting a legacy system that has been highly modified with reference to posting Job Revenue Recognition. The new system (Navision) #1 doesn’t calculate the same way & #2 Customer has many open Jobs that will span the conversion/cut over date. Customer is leaning towards running both systems simultaneously: 1 - Legacy for Open Jobs, until all have been closed, 2 - Navision for new jobs that “open” after the cut over date. Due to the spider-web effect the Job related entries have on the sytem, this option posses many issues: errors, double entry, time consuming, Tie both systems together would then be necessary on a regular basis until all jobs have been completed in old system (6-12 months). There’s got to be another way to handle this situation!! I have dealt w/ Inventory Costing Changes and the client will usually “agree” to change the way they calculate inventory: do the cutover, make an adjusting entry to Inventory accounts as necessary, but then move forward allowing Navision calculate how it wants to from that point forward. I feel that this is our only option at this point. BUT how to handle the Job Recognition for open entries prior to cutover . My thoughts are run periodic activities prior to cut over. Post entries to G/L. Cut over. All entries made to Jobs after cut over are recognized the new way. Suggestions, thoughts, ideas?? Thank you very much. D