I have a colt officers target model revolver built on the 41 frame.
What grips fit this? What letter frame is it? It's a larger frame.

It's an E frame. In Python and other .357 pistols, it's an I frame, but the grips are the same for both. Pachmayr used to make grips for them, even with an authorized Colt medallion.

I have the pachmeyer grips it came with used. I'd like to get wood grips.

Look here for the several variations of the OMT. Officer's Model
If you indeed have an OMT (and not the OMM) it would have originally been shipped with the standard checkered wood service stocks as shown. The later Officers Model Match (OMM) revolvers often came with various designs of target stocks which may be extremely desirable and improved adjustable sights. I have one of each, and they are both superb revolvers, just like the third and fifth pictures in the link.

Replica service grips are easily found. Good originals, not so much, and they will be expensive. Look on ebay.