Some 74 blocks do not accept the old mounts. When the previous owner installed your engine he must have rigged it in some way to fit. That's the only explanation of why the oil pan would be hitting the frame. If you could get a picture of the mount we could tell you what's up. ****One other thing I just thought of is if your trans mount is too high it could possibly change the angle of your engine to make it low in front.
Jim