
That is a very nice tank that I put in (24 gallon), you might want to measure how thick it is vs. a stock one. Either style of stock tank is going to need a good skid plate or they will bend. I think Kilby enterprises makes a good aftermarket skid for the 20 gallon tank.....
Also, your electric fuel pump is in the tank so you are going to have to mount an external one on the frame rail.
Here one that I found a link for in POR.
External mount MPFI fuel pump.