grammar - Relative Clause Extraction from Subordinate Clause - Compare and Contrast These Sentences

Please emend the title; I'm tentative whether it summarises this question precisely.

1. 
   

   I went into the store, which if I had seen from the road, I should have known to be a company.

   
   


2. 
   

   I went into the store, which, if I had seen it from the road, I should have known to be a company.

   
   


3. 
   

   I went into the store, which if I had seen from the road, I should have known it to be a company.

   
   


4. 
   

   I went into the store, if I had seen which from the road, I should have known it to be a company.

   
   

1 seems the most natural to me. Would someone please compare and contrast the other 4? Are they grammatically correct? If so, how are they?