It's a 1969 model year engine unless you can see the first digit in the vin to prove otherwise. X heads, march 69 casting, "E" in the model year stamped on front of engine representing a 1969. If it was an F, then it would be a 70 model year engine.
IMO, little to no chance an engine would have sat for 8 months to 1 year coming out of that assembly plant to be that late in the 1970 model year, seq 255 = mid Feb 1970 spd's. There was a shortage of 340's in Dec 1970 model year production coming from windsor engine plant. My 1970 December built swinger 340 has an engine that is assembly dated 2 weeks after the December SPD.
Can't be an august 1969 cast engine if it was assembled in April 1969.