If you are using the same plunger and thumb safety you had in it before and it worked okay then, I would suspect something else - the fit of the safety to the parts you changed, specifically the sear.
Although it's often thought parts for a 1911 are a "drop in" fit that's not always the case, especially when aftermarket parts and/or a non- mil spec gun are involved.
When the safety is put to the on position the tail end of the sear fits into a notch on the safety which prevents movement of the sear, hence rendering the gun safe. The specs of the aftermarket sear may be slightly different than the original causing the "binding" when you try to move the safety to the off position.
First thing I'd do is compare the two safetys to see if there is any difference that can be seen. Also look closely at the safety to see if there is any evidence of rubbing of the sear to the safety.
The aftermarket safetys I've installed (extended models) have came oversize in this area and had to be fitted to the sear. This requires very SLOWLY removing a TINY amount of metal from the safety so it will clear the sear to move from on/off or off/on positions. Of course if too much metal is removed the gun is unsafe and you have to start over again with a new safety (how would I know this???).
Don't know if that's the cause, but it's something to check out.
