Damper Disappointment

I have a 69 / 340 did the water pump swap, drivers side to passenger side. front cover changed for timing marks
On drivers side. Replaced original damper due to age & slight deterioration of elastomer.
Replaced with this,
20201026_183441.jpg
Got around to checking timing Mark's on the new damper with Mark's on drivers side. There way off.
Put the stop in #1 cylinder, turned engine clockwise on the compression stroke. When it stopped it read 20 degrees at the 0 mark on timing cover.
Then turned counter clockwise untill
it stopped, dampers 0 mark was at
10 degrees ATDC on timing cover.
Can I just find center between the 2
mark's & make the correct 0 mark on
damper the use timing tape over the
Damper? Any help or advise appreciated.