Insert Rows And Add Formula?

Looking for some code to do as follows...

Data as is:

Data 1
Data 2
Data 3
Data 4
Data 5
Data 6
1
2
3
4

123
567
A
A
A
Data 1
67
88
39

So an extra row needs inserting below the last record of each Data 1, with each value in Data 1 through 5 coming from the record above, but Data 6 is called "Diff.". The values in columns 1 through 4 for "Diff." are then driven by the following formula:

=H3-H6

Obviously then copied across.