Can a 6-cylinder ranger transmission fit in to 4-cylinder ranger?

No, a 6-cylinder Ranger transmission will generally not fit into a 4-cylinder Ranger. While they might share some superficial similarities, the bellhousing (which connects the transmission to the engine) and the internal components (gear ratios, shaft sizes) are different and incompatible. Even if you could physically force it in, it wouldn't work correctly and could cause significant damage.