Dear baachitraka,
If you are willing to make the step to tripods and spotmeters, why alter your OM-1? It is a well sought after camera and you will only reduce the value. An inexpensive 645 will make much better photos and you can keep the OM-1 for those times when a tripod is inappropriate. Trust me on this one (I sometimes use an old press camera for walking around when I'm willing to put up with the questions), a spotmeter (or any non-coupled meter) is not nearly as handy if you ever need to work quickly. I suggest trying it out a few times before modifying your camera. You can sometimes find an old Soligor spotmeter for well under $100. I have one and, while it's not as good at low light as the better models, I have made plenty of good exposures at all times of the day.
Good luck,
Neal Wydra