What timing cover are you using with a 7.3 inch damper

I thought a 273 was an early SBM.
The cover shown is a very late one.
The balancer appears to be keyed for a passenger side tab.
If it was my problem, I'd mill off the Driverside tab and mig the hole closed. Then install the balancer, shimming it out as may be required, then Find whatever piston-TDC gets you in the ballpark on whatever side you care to use, and index the cover accordingly. Then when you go to set the timing, don't forget which piston you indexed.
Badaboom.
In your case with a calibrated balancer, you don't need a tab anyway; all you need is a fixed stationary reference point somewhere with any appropriate piston at TDC, that gets you visibility to the mark, with all the accessories bolted on.
I have had to, on old Dodge vans, put the mark on the very bottom and read the timing while laying on my back.
On others I had to take the doghouse cover off, and drill a hole in the Bellhousing, put #1 at TDC, then scribe a mark on the convertor in the center of the window.
Whatever it takes. The mark can be wherever you want it to be. Well, with an indexed Balancer, you are sortof limited to four places, two of which you will need to stand on your head to read, lol.
If that's not good enough well, you can always put a timing tape over it.