Some manual valve bodies have the stem that the throttle pressure linkage lever slips onto cut off so there's no way you could put linkage on it. You can tell this just by looking at where the throttle pressure linkage arm attaches to the valve body right above the shift linkage arm.
As for telling by dropping the pan and just looking at the valve body probably not. I have only seen a few manual valve bodies and they were all factory valve bodies that a company (TCI, etc) modified. They generally put their name and their part # stamped on it somewhere but sometimes it's on the top side so you won't see it by just dropping the pan, you may have to drop the valve body also and look on top.