I am helping a buddy swap a 318 into a 66 Barracuda that had a 273 in it.
The 318 motor he bought came with a damper where the timing mark is straight in line with the crank key way.
The bottom pulley he took off of the 273 but when we went to install it, it would not fit onto this damper because the bolt holes did not line up.
I had an old 318 damper lying around that we compared to the one he got with his 318. My damper has the timing mark around 90 degrees to the left of the crank key way and the bolt holes lined up ok with the pulley. We then compared my damper to the old one that is still on the 273 and they are a match.
Now, we noticed that the 273 has the front cover timing marks on the right side (passenger) and the 318 has them molded into the front cover on the left side.(driver)
I just want to confirm that the damper with the timing mark 90 degrees off of the key way will be correct with the left side timing marks on the front cover.
Can anyone help me?
Thanks.

most important is what radiator will you be using, An OE one (or like the OE one, with the lower hose on the DR side & in that case I would use the 273 t cover/dampener/pulley with the marks on the pass side & you can elongate the one bolt hole in the pulley that is slightly off. You can see the marks with the hose/timing marks on the same side if you aim the light just right but it is easier to have em on opposite sides. More info please on where you are at on this. You referred to the 318 t cover marks being straight in line with the crank keyway, did you mean with the keyway at 1:30 (TDC) the t cover marks are above em?

Mopar swapped the lower radiator hoses from the driver side to the passenger side in 1968 or 1969 on all the LA SB motors, CRS. They had to change the timing gear cover and balancer timing marks so you can see the timing marks on both from the driver side. Use the balancer, timing cover and pulleys with marks on the side your radiator works with
You can oblong slot the one hole in the early lower pulleys to use it on the 1972 and later symmetrical dampeners
It takes about .130 or so material removal, it is done all the time

Thanks guys.
He did get the water pump that puts the radiator hose on the drivers side but he left the front cover with the timing marks on the driver side too. Might be hard to see.
We did oblong one of the holes on the pulley.
Thanks again.

on the same side deal, it helps if you make several white paint marks on the dampener CW from the OE timing slit. (5) is plenty, 10 12.5 15 17.5 & 35 for total. Use the dampener as a ruler and 2 & 1/4" is 35.5 degrees, (close enough). EDIT It might be easier (if you do this) to get the OE slit on the bottom so you have room to work & make your marks. (1) degree is 0.0632683" & just do the math & cut a strip of white paper & measure/mark it with a sharpie then use it as a ruler to make marks on the dampener.

The breaking point was 69 and earlier,cast iron water pump and then 70 and up aluminum water pump.