Pontiac blocks are easy to identify if you know what to look for. It is simple, for example, to visually categorize all 1959-and-later blocks into 389/400 or non-389/400. All displacements other than 389/400 possess a "transfer lug" (found at the rear of the block shaped like a "mountian" or "pyramid"). There are only two exceptions: the 1961-62 421 SD (the same blank casting as the 389) and the 1973 SD-455. All V8 blocks cast prior to 1959 (287, 316, 347, and 370) were "standard" displacement and did not have a transfer lug. In addition, these 1955-58 blocks did not use side-mounted motor mounts as did all blocks from 1959 forward. All blocks through model year 1963 have a production number cast into the passenger side of the block. The casting number for these blocks are as follows:

1955 (287 c.i.d.) #518037 1956 (316 c.i.d.) #521560 1957 (347 c.i.d.) #523293 1958 (370 c.i.d.) #528456 1959 (389 c.i.d.) #532000 1960 (389 c.i.d.) #536387 1961 (389 c.i.d.) #538181

1961 (421 SD) #538181 1962 (389 c.i.d.) #538181 1962 (421 SD) #538181 1963 (326 c.i.d.) #548211 1963 (389 c.i.d.) #543680 1963 (421 c.i.d.) #544988

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Beginning with the 1959 389 c.i.d. blocks, side motor mounts were utilized for the first time. Two motor mount holes appear on each side of the block, a feature that would continue through 1969. Beginning in 1964, all blocks were cast with provisions for block-mounted starters, even though most of the large cars still used the bellhousing-mounted starters. The block casting number location moved from the side to the distributor pad (except for the 421s). All the blocks cast through model year 1964 included cylinder head stud oiling passages. No engines after 1964 utilized the stud-oiled heads, so these passages were eliminated in 1965. All blocks from 1955-66 used two freeze plugs per side. Block casting numbers for the 1964-66 engines are as follows:

1964 (326 c.i.d.) #9773153 1964 (389 c.i.d.) #9773155 1964 (421 c.i.d.) #9773157 1965 (326 c.i.d.) #9778840 1965 (389 c.i.d.) #9778789

1965 (421 c.i.d.) #9778791 1966 (326 c.i.d.) #9778840 1966 (389 c.i.d.) #9778789 1966 (421 c.i.d.) #9778791 early 1966 (421 c.i.d.) #9782611 late

All blocks are cast with a date of production code. This code appears on the distributor pad. The code consists of a letter, followed by two or three digits. The letter signifies the month (A = January, etc.). The letter "L" signifies December for all years but calendar 1966 (1967 model) when the letter "M" was used for December. Since "I" was used in all years, it is possible that both "I" and "J" were used to designate September. The reason is not known. The 2nd character in sequence (or 2nd and 3rd if three digits appear) is the day of the month. The last digit designates the year of production (not necessarily the model year). For example:
A #9773155 block with a date code of J23 = October 2, 1963.
A #9782611 block with a date code of F126 = June 12, 1966.

All blocks produced for model year 1967 were recast for three freeze plugs per side. Beginning in mid-1967, the block casting number changed location from the distributor pad to the rear of the block, just behind the #8 cylinder. The foundry line casting can be found in two places, on the front side of the block (GM1, GM2, GM3, etc.) and at the extreme rear end of the block on the distributor pad (1, 2, 3, etc.). In addition, 1968-69 428s received two additional displacement identifiers, a cast "428" on the side, and a "28" cast into the center lifter valley rib. Similar identifiers would be used to identify other displacements (455, 350 in 1970, and 400 in 1971). Casting numbers for the 1967-69 blocks are as follows:

1967 (326 c.i.d.) #9786339 1967 (400 c.i.d.) #9786133 1967 (428 c.i.d.) #9786135 1968 (350 c.i.d.) #9790079 1968 (400 c.i.d.) #9790071 1968 (400 RA) #9792506 1968 (428 c.i.d.) #9792968

1969 (350 c.i.d.) #9790079 1969 (400 c.i.d.) #9790071 1969(400 RA IV) #9792506 1969 (428 c.i.d.) #9792968 1969 (303 c.i.d.) #546313 1969 (400 RA V) #9792968 1969 (400 RA V) #545887

In 1970, all blocks received three additional motor mount holes for possible mounting in the new Firebird chassis. In some cases, only three holes were tapped, but five pads were machined. Blank block castings for 1970-76 are as follows:

1970 (350 c.i.d.) #9799916 1970 (400 c.i.d.) #9799914 1970 (400 RA III) #9799914 1970 (400 RA IV) #979991(5) 1970 (400 RA V) #481708 1970 (455 c.i.d.) #9799140 1971 (350 c.i.d.) #481990 1971 (400 c.i.d.) #481988 1971 (455 H.O.) #483677 1971 (455 c.i.d./late H.O.) #485428 1972 (350 c.i.d.) #481990 1972 (366 c.i.d.) #(485)212 1972 (400 c.i.d.) #481988 1972 (455 c.i.d.) #485428 1973 (350 c.i.d.) #488986

1973 (400 c.i.d.) #481988 1973 (455 c.i.d.) #485428 1973 (455-SD) #(490)132 1974 (350 c.i.d.) #488986 1974 (400 c.i.d.) #481988 1974 (455 c.i.d.) #485428 1974 (455-SD) #(490)132 1975 (350 c.i.d.) #488986 1975 (400 c.i.d.) #488986 early 1975 (400 c.i.d.) #500557 late 1975 (455 c.i.d.) #500813 1976 (350 c.i.d.) #488986 1976 (400 c.i.d.) #500557 1976 (455 c.i.d.) #500813