Hi Flump,
these are logic ICs which contain some dividers. First page of your PDF explains what you need to do:
A symmetri-
cal divide-by-ten count can be obtained from the
DM74LS90 counters by connecting the QD output to the A
input and applying the input count to the B input which
gives a divide-by-ten square wave at output QA.
To-do: Turn your 10 MHz sine from OCXO into a logic level signal (TLL, as rectangularish as possible, anything which goes belov 0.8V and above 2V is sufficient. This signal should go into input B of the 74LS90, on QA comes the 1 MHz Signal, also a 5V logic signal but with 1 MHz.
Clip, attenuate, higpass filter the output until it fits the requirements of your counters reference input.
Alternative pathway, you might consider buying a QH40A xtal heater from Kuhne electronics (DB6NT, around 12€) to temperature-stabilize your internal references xtal, and check if it is already more stable. If the internal reference has a trimmer for adjustment you might consider reducing the trimming range.