1995 sambar engine swap problems

Add the title states I swapped a customer's engine due to a badly blown gasket and I'm more in the process of trying to get it running. My first concern was that the engine that was provided had an extra oil drain return on the oil pan and bent ooc the valve cover that weren't on the original engine. This model is a carb version and it sat for about 3 months waiting on the new engine. Now after getting it in I just can't get it to start and I'm getting kickback through the intake even after verifying the mechanical timing and firing order of the cap and wires are correct. Wrong engine or steps to diag a bad carb would be helpful.