The serial numbers for 1934 engines are just under the 3 million mark. Your serial number is over 7 million. The last digit is a suffix indicating car series (-4 = series 40 Special).
Production of the final year for Buick straight eights (1953) began with engine no 6950620 and carried on through the run of about 220,000. So your engine is a '53 model 263 cid.
Series 40 Buicks in 1934 came equipped with a downdraft carb while series 50-60-90 cars had an updraft carb.
What has been, can be again. (Bob Wills, 1942)