Ok so i gotta replace the oil pan gasket again but with the motor in the car i been doing my search method first an saw that if i use the one piece oil pan gasket i dont have to lift the motor up just drop the pan down on the cross member make the mating surfaces dry put the new one on an bolt everything up also do i have to use the oil pan rails from the factory cause i saw on my stock 350 it had them on it an my 355 doesnt ???

 

first, a 355 is a 350, it's just been bored to clean up/true up the cylinders

second, i don't know where you've been reading but you need to lift the engine some to get at it well enough.

It's duck soup
put vehicle on ramps or jack stands (5 minutes)
remove 2 motor mount bolts (4 mintues)
remove nut from tranny mount (2 minutes)
wheel engine hoist over engine and attach chains (5 minutes)
lift (1 minutes)

go underneath and drain the oil and get to work

oh, disconnect the battery because you're near the starter and don't want to go ZAP

 

As far as the rails go, they are a good idea as they spread the tension over the surface to maintain good seal with the rubber gasket.