Oil pan replacement?

[85chevyk10]

Just got a 85 K10. It had a 305 originally that was swapped for a 350. I tried to replace the oil pan today but the holes didnt line up! Also I ended up buying 2 different gasket sets and neither fit on the bottom of the motor... I am trying to figure out if maybe I have a pre-80s chevy 350??? Trying to get this oil pan replaced because it was leaking horribly and the plug was stripped really bad. Any knowledge would be really helpful!

[bake74]

    You will need to look on the block behind the drivers side head at the back of the engine and find the block Id #, then you can find out if it is really a 350 first, and what year range it is.