I don't own one but .....
I made a radial arm router from a radial arm saw by replacing the saw carriage with one that holds a PC 690 router. See My Photos. I haven't found it particularly useful at this point even though I made some mortises and tenons and a key slot as trails.
Would a overhead pin router be feasible for styles and rails ..... I wouldn't think so, but as I said I don't own one. You would have to invert your thinking process because you are now working from the top down as opposed to using a router table. For some bits it wouldn't matter, others may ... I donno? The material definitely would have to stay put on the table, even more so than on a router table ... just my opinion. I wouldn't want to do panel raising with the cutter overhead, just too dangerous.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)