Anything made by OS or HPI is a good bet as long as it has the same carb style. The LRP .18 is a strong little engine as well. However, you can rebuild the stock one in it for under $40.
With how light that things rear end is, and how much power big blocks put out, there is no reason to even consider the swap, unless you just plan on asphalt riding. Couldnt catch traction on anything.
I have to agree, that would be like driving on ice with racing slicks. But if you really have your heart set on it, you would need new tires I would think.