Jimm. You might want to check the specs carefully on the M2 chassis. My impression is that the basic M2-106 is the replacement for the FL-70. It has the lower cab height but also is limited to a C-7 Cat engine at 300 hp and 860 lb torque.
The back of cab to front bumper length is about 8 1/2 feet.

If you want a larger engine, possibly with the tandem, you go to the M2-111 which is the replacement for the FL-111. This might have a higher cab. I believe the bumper to back of cab length is 10 feet.

Again I am not exactly sure of all the specs but I remember somewhere seeing two sizes of M2. But I also could be mistaken.
If you find out please post the correct info.