I personally would prefer 2 hours minimum to connect from an international flight in DTW. My experience in getting through customs and re-screen security you can push the 45-60 minute mark and I always fly buisiness class, so I am in the front in the plane. It can be done within the 70 minute window but you to plan for late arrivals and such... The good news is that Flt 71 usually leaves from one of the gates near the exit from customs & immigration.

Because you are on two separate tickets I am not sure that you can check luggage all the way through to MNL and you may need to allow time to recheck it before your next flight. If you can not check it all the way through then I would just do a carry-on, as I do not recall facilities to re-check baggage with other airlines down there. (I am not usually looking for that service though).

DTW is actually a pretty nice place to hang out also, there are a lot of restaurants and shops to occupy your time.