[LPI]

The 1967 and 1968 2 bolt main blocks are very similar in structure and strength.

In 1969 they started decreasing the material in the webbing and continued doing so each year there after. If you set up a 1967, 1968, 1969, 1970, 1971, 1972 and 1973 blocks each one will have subtle changes in the main webbing area. In all cases the webbing gets thinner as the year of the block gets newer.

Another item to watch out for is the letters stamped on the oil pan rail. If there are letters stamped by the main cap webbing on the oil pan rail you better measure twice and cut once or you will be sorry. Again another item that gets blamed for engine/bearing failures when in most cases it is a measurement error.

I have the revision list from 2/69 thru 7/72 which shows most of the changes and updates over the years on these 9799 thru 485 blocks.

The actual material used was Cast Iron - G.M. 232-M

One of the reasons why the main caps break or crack at the dowel pin hole is from switching from factory bolts to ARP/Milodon studs. Studs and 4 bolt mains are not better unless you look at all of the parts and each individual application.

Another note. GM did not use "standard" diameter dowel pins in the main caps.