It really depends on the build date of the chassis. Earlier builds usually have more scattered dates with all components (starter/alt/waterpump/distributor etc.) The blocks/heads/intake/exh. were usually spaced 2-3, sometimes 4 weeks apart. 1967's were mid year start in January...Not uncommon to see a B coded block with A coded heads in a D coded chassis.

The later in the model year typically had more tighter dates. My 1967 December built 68 has dates for rear end, engine, heads, intake, trans...all cast within 7 days. L177 heads L157 intake L187 block..L157 rear end.

Rationale? They had surplus of parts from prior model year plus a huge run of parts built to start the line.

The BEST way to solve this? Find a true, low mileage survivor, same year, same driveline with documentation close to your build date. Document the dates and compare.

Alot depended on the shift working at Lordstown. I have read and heard about workers on certain shifts so concerned about keeping the dates close for all engine components wheras another shift was not so concerned.