I am attaching a ledger for a 2nd floor framing system to a ballon framed farm house cira 1840, with rough cut 2x4 studs with german lap siding on the exterior. The design was to attach the 2x12 ledger thru the siding with 3/8" lag screws 2 per stud. the studs are 16" o.c. 20' engineered wood...