Timing Chain Cover

I am not able to use a T bolt, the whole upper half of the mounting hole broke off. Good idea to try, but unable to with this.
Went out today and looked for numbers and this is what I found:
1. Stamped number on end of drivers side head: A 273 - 11 - 5
2. Casting number on drivers side of engine block: 2465330 - 1 ( From what I have been able to figure out this number is for 273 LA - series small block made between 1964 and 1966.)
3. Numbers I found on block on passenger side: 10 - 30 - 6 ( Do not know what these numbers mean.)
So I guess that if I can find a timing chain cover without the timing mark cast on the cover would be nice. If not I will just bolt the removeable timing mark gauge and go on down the road.
Any additional info about the numbers or other thing to check is appreciated.
If that A273 is on the block and not the head, it's a '65 273 with a Nov 5th build date. I suspect that block casting date is probably 10-30-5 and not 6. Sometimes the numbers are rather crude and hard to read.