Hey I think I have an early 70 - 75 block here but it has a 8 bolt water pump. photo is of the stamp at the bell housing
This has probably been covered before so apologies but I’ve searched a bit an 8 bolt was 68 maybe 69, then 11 bolt onwards. 
my question is why would an 8 bolt be on later block ? Is it just because the 8 bolt timing cover fits on the later blocks ?

Google is a bit of a arse for this kind of thing, people are better. 

You have more ID #'s on the front of the block next to water pump on  Pass side.  Worth keeping the link for future ref.                 https://wowmusclecars.com/pontiac-engine-codes-specs/

I can think of a couple of reasons.
 

The water pump cover is not original to the engine and it was replaced by an earlier model cover using the 8-bolt pump. This suggest that the original cover was damaged and replaced for some reason.

Second scenario is the the engine itself it not original to the car and the engine came with the older style water pump.

Thanks for that link it’s really good justa6.

frosty I did not know the earlier timing covers could be used on later blocks so cheers for that. 

Yes. For the longest time, water pump/timing chain covers were not reproduced. So you had to scrounge around for a good used replacement , 8 or 11 bolt. Now they are being re-popped so getting a new one is a lot easier.

Edited September 7, 20241 yr by Frosty

Hey thanks Frosty

I have a new cover now… I you don’t mind I have one more question. Is there any need for the three bottom bolts on the water pump to be studs ?

I got one stud out from the old cover and it has different thread to the new cover so no go. 
Are you able to just get replacement bolts or are studs there for alignment / torque and things 

Interestingly to me, the three stud and nuts are different thread pattern to the five remaining bolts 

thank you 
 

Hi Doug! Happy to help.

The studs are typically used for mounting / hanging accessory brackets like AC, alternator, and/or power steering pump brackets to the front of the engine. You can replace them with bolts but it might make mounting the brackets more of a challenge. You can get replacement bolts from ARP and I'm sure other commercial sources as well.  Sundell Auto sells refurbished original bolts.

 

https://sundellauto.com/products/1965-72-pontiac-gto-lemans-tempest-timing-cover-bolts

 

Edited October 7, 20241 yr by Frosty