Hello Marco,
Welcome to VCCA Chat. Based on your post it appears that you are new as well as older Chevy's.
I am not an expert on '36 Chevy's. However, it would surprise me if that year car required that the engine be removed to remove the oil pan. It was not unusual to remove the oil pan to adjust the main and rod bearing clearances as well as clean out the oil pan and make sure that the oil dipper troughs and dippers were adjusted correctly.
I strongly recommend that you get access to a service manual to help you as you work on this engine.
I also suggest that you make sure the problem is just an oil pan gasket leak. There is no seal on the rear main bearing. It is a slinger design. If the rear main bearing clearance is too great that creates a major oil leak. These old engines have lots of places to leak!
