Do NOT cut the front off of the Magnum one piece gasket. No need to. Ever.
Some aftermarket oil pans do not fit correctly with their proper gasket. I recently had a Milodon pan that the little holes for front seal were so far off the rubber would never seal between the pan and timing cover. Similar to why the OP cut those nipples off.
Never use grease, oil, or anything else on oil pan gaskets that prevents RTV silicone from sticking. It will usually leak. The silicone will act as a lube and help it slide in place, then glued it there once dried.
Best bet here is to use the one piece Magnum gasket, fill the corners with silicone, then make damn sure the front rubber part is properly positioned while tightening the bolts down, and tighten a little at a time. The Magnum pan has a wide flat loop on the front where that rubber sits. The LA pan is narrower and usually has an extra ridge on that loop that presses on the wider LA rubber, but the LA rubber has flaps that keep in place.
You need to make sure that front Magnum rubber stays centered until everything is tight, and it usually works.
My pictures of this are all on a flash drive somewhere but I will try to find them when I have time.
