How many hours to remove and install a Cherokee 180 engine and prop
I once changed an engine in the bush when I was bush flying, helping the air service's mechanic.  It was a C-180 on floats (I had been forced down in it after the engine developed a loose cylinder from failed hold-down studs).  

There was a rigid dock for us to work with at the remote lake we were at, and we used a bipod made of pine poles with a come-along to lift the engine and set it down on the dock (with the noses of the floats against the dock).

It took about 6-7 hours to have the engine and prop removed and ready to be loaded on the company Beaver when it showed up around 5 pm (loading it was the really entertaining part).

We went back in two weeks later with an overhauled engine and installed it, 2 mechanics and myself, and I flew it out that late afternoon around dinnertime.

So for a Cherokee sitting in a hangar with a lift handy, one mechanic with an assistant, about 4-6 hours to remove the engine, and about 6-8 hours to install it.  Certainly no more than two days at most.