I have done multiple modification on ASM and Euroreef for my friend. You will need 2 uniseal 3/4" for the return and 1" for succion, 2 unions 3/4" and 1". Your existing hole will be use to feed the skimmer either via a small pump or your drain. Since the base of your ASM small, you may need to fill the skimmer up with water before it can stand on it own. Unless you build additional leg for it. For more information, send me an PM and i can help explain better.
Thank s
STeve