First thing you need to do is confirm where it is leaking from. Could be the rear main or it could be the oil pan, rear rocker covers, block plug, etc, etc. Get a dye kit from a parts store and verify the leak.
Don?t know what year your 454 is but if it is a rear main they used 2 piece seals until the 90?s then a one piece. One needs the pan pulled, the other needs the trans pulled. If you do have to replace there are many things you need to follow specifically such as cleaning and install methods or you will learn on your 2nd or 3rd try. If the seal area is damaged you can get a special extended seal from the parts store to put the sealing area in another position. If the rear is bad I would also check PCV or whatever your engine is using to vent the crankcase. Usually the front main goes first is this case but again, you need to clean everything and verify exactly what is leaking. I?m going from memory on this but there is plenty of info on replacing seals etc. depending on what you find. Good luck and welcome to the forum.