The 3970010 casting number was used for two sizes of engines:
1968 327 and;
1969 – 79 350.
This casting could have 2 or 4 bolt mains and was used in everything from trucks, to sedans to high performance applications. The numbers on the front pad are the key if you want the specific application (see my answer in your other thread).

460776 is a 305 made between 1976-79. Fairly “vanilla” motor.

Neither of these casting numbers are associated with a roller cam.

As to nickel content, the following is from the nastyZ28.com web site:

"Tin and nickel are two metals that are commonly alloyed with cast iron to improve durability, hardness and heat dissipation. Some production engine blocks have the numbers "010", "020" or both cast into their front face, just above the main bearing bore. (The timing cover must be removed for these numbers to be visible.) If both numbers are present, one about the other, it indicates that the block alloy contains 10% tin and 20% nickel. A single number, either a "010" or "020" represents the amount of nickel and indicates negligible amounts of tin. No numbers, other than the casting numbers that are typically found beneath the timing cover, translates to only minor amounts of tin and nickel being present in the block alloy."

However, cylinder wall thickness should be your primary consideration - and a block with no tin or nickel and thick cylinder walls is generally preferable to a high nickel block with thin walls.

Regards,
Glenn