benjo

I've just bought a 1995 Yamaha Sr125 off of ebay (will be my first bike). I bought it as a non runner. The cam shaft is starting to wear, thus making a bad noise and engine has seized, looks like the owner neglected to maintain the correct level of engine oil. I have decided to try and get a second hand engine. The ones i have found have been from newer bikes. Will an engine from a newer bike, say 2000, fit straight onto my bike with no mods to the engine or bike? Any help will be greatly appreciated.