I have a 70 engine in a 68 Barracuda. I made the assumption I needed a 70 balancer because the crank is keyed for one. I wanted to put a 68 timing cover but used a 70 in lieu of. The question is, will a 68 balancer on a 70 crank move the timing mark to the passenger side?
If you have a real 68 balancer the timing marks on it will be on the passenger side. You will need to remark it, or just time it by ear.
I think the 66-68?? LA 273s and 318s had a bolt on timing tab that you can also use to solve that problem. I had one on mine for awhile. They are hard to find, but usually only $20-30.
You could buy a new one marked properly, but you need to make sure you get one matched to your crankshaft. I think the cast crankshaft started in 72 or 73. With a 60 year old engine, who knows what is in it…