Are you sure its a 261? Nova's never came from the factory with a 261 or 235. From the factory in 62 it would be a 194ci. Direct replacments for the 194 is a 230 or 250. It appears from the casting number that's what someone did. If it is a 261 there would be modifications needed to get it in. I also own a 62 Nova. The 230 and 250 has a bore of 3.875 also.
Terry
Novaconv
