Timing Chain Cover crankshaft opening is the wrong size
There are at least 3 timing covers.
67(maybe 64) to 68 no timing marks on the cover. Seal installs from the inside (Uses a bolt on timing mark on the pass side)
69 one year only. Timing marker is part cover BUT on the pass side (red)
Seal installs from the inside (green) smaller external opening
70 to 73? timing marker is part of the cover and on the driver's side. Seal installs from the inside.
73? And up timing marker is part of the cover and on the driver's side. Seal installs from the outside (this one has a 78 date mark on it)
Somewhere the the seal went from installed from the inside to the outside.
Inside seal is smaller then outside seal.
Rock Auto suggests 12/72
If you have a 68 setup and 68 damper it should have a bolt on timing mark on the passenger side.
You mentioned the block is a 73 and I assume they used the 73 damper. If so you have to use the 70 up cover, or change the damper to a 67-69 style and get a 67-68 cover and marker.
BTW...
The 69 and older damper timing mark does not line up with the 70 up marks on the cover.
There are at least 3 timing covers.
67(maybe 64) to 68 no timing marks on the cover. Seal installs from the inside (Uses a bolt on timing mark on the pass side)
69 one year only. Timing marker is part cover BUT on the pass side (red)
Seal installs from the inside (green) smaller external opening
70 to 73? timing marker is part of the cover and on the driver's side. Seal installs from the inside.
73? And up timing marker is part of the cover and on the driver's side. Seal installs from the outside (this one has a 78 date mark on it)
Somewhere the the seal went from installed from the inside to the outside.
Inside seal is smaller then outside seal.
Rock Auto suggests 12/72
If you have a 68 setup and 68 damper it should have a bolt on timing mark on the passenger side.
You mentioned the block is a 73 and I assume they used the 73 damper. If so you have to use the 70 up cover, or change the damper to a 67-69 style and get a 67-68 cover and marker.
BTW...
The 69 and older damper timing mark does not line up with the 70 up marks on the cover.