This is an application code and is NOT a part #!!
In fact the application code should be differ from the part # usually found on the the float bowl.

The application code breaks down into three basic parts.

The first two digits "70" indicate the manufacturer; Rochester Products Division of GM.
NOTE: Beginning in 1975, this was changed to "170".
IMPORTANT: "70" (pre-'75) and "170" ('75 on) jets, rods, etc. are alleged to be
NON INTERCHANGEABLE!

The next two digits, "41" in this case, make up a date code. The first digit is a decade code, and the second digit indicates the year.
Remember that for 1960 and on, the decade code is an even number starting with "2".
"2" = 1960, "4" = 1970, "6" = 1980.
So, "41" indicates 1971, and "25" indicates 1965.

So, 7041251 is a 1971 Rochester Carburetor.

Here is the really sticky part. The last three digits make up an application code of sorts. Karl has seen little info on deciphering this, so take the following as possibly being just nonsense! Karl hopes to clear up the matter with info from GM.
Note that different codes mean different applications, and carbs for different applications will have different jets and metering rods.

"251".

"2" - Karl not know for certain. It appears that this digit became a indicator of the carburetor model, Monojet, Dualjet and Quadrajet.
It seems that the numbering system varied by year, making the codes tough to read.
Karl two 2-Jets, one a 1964, one a 1965. They have a "1" and "0", respectively, for this digit.
A Mr. Padgett, whom is linked to below, has "published" an interesting treatise on this topic called "How to Speak Rochester".

"5" - This is alleged to indicate the GM division as follows:

0-2 Chevrolet or GMC
3 Cadillac
4 Buick
5 Oldsmobile
6 Pontiac

"1" - This last digit indicates which specific motor configuration that the carb was intended for.
Unfortunately, there does not seem to be an easy way to decipher this.

On Oldsmobiles, this digit tends to increase with performance level;
"1" might be a 350 AT
"2" might be 350 w A/C
"3" might be 350 MT with performance options
"4" might be 455 AT

So 7041251 is likely to have originally been on a 1971 Olds 350!

However, the code on Buick carbs seems to be the exact opposite of the "trend" for Oldsmobile carbs! Example: for 1969 Buick carburetors:
"0" was 430 AT
"2" was 400 AT
"3" was 400 MT
"4" was 350 AT
"5" was 350 MT

But it's not so bad because there is some order.....right?

Wrong!
The codes keep changing!

Beginning in the mid-1970s (???), especially in the emission control years, there are code numbers for carbs that went onto California cars. If the manufacturer switched to a slightly different carburetor during the model year, then that would generate yet another code number!
A good example is Rochester codes for 1976 Oldsmobiles:
"250" was 350 AT
"253" was 350 AT with A/C
"550" was 350 AT for California
"553" was 350 AT with A/C for California
"258" was 350 AT on late 1976 cars
"259" was 350 AT with A/C on late 1976

Note that the CA carbs have a "5" as the fifth digit (really the sixth digit because 1976 used "170" codes).