badazz81z28

iTrader: (6)

If you have a "Mystery" LS1 meaning no car which to base the year off of, How can you tell if it takes the older or newer style head bolts?

BlackScreaminMachine

iTrader: (17)

Generally casting numbers off the block. Look towards the rear, near the lip where the bell house meets the block. Search here or Google.

As for bolts I would think it does not matter as your going to use ARP, no?

https://summitracing.custhelp.com/ci/fattach/get/44974/

^ Very Helpful

thunderstruck507

iTrader: (18)

It matters because there are 2 versions of the bolt sets. 1 are all the same length and the older ones which are 3 different sizes.

NC98Z

iTrader: (1)

I believe you got that backwards. The older models had the same length long head bolts and the later models had the different length. The easiest way to tell would be to measure the hole depth with a pipe cleaner and see if some of the block holes are shallower.

badazz81z28

iTrader: (6)

Go figure, my casting is 12561168, which shows it can be either way. Is there a Month/Year some where on the block?

bww3588

iTrader: (49)

The older blocks had 3 sizes, the 04 up blocks had 2 sizes. Easiest way to tell is stick something in the holes and see. The holes on the ends of the block will be deeper than the ones in the middle.

gMAG

iTrader: (1)

Yes, sir!
I'm looking at mine right now (older block) from a 98.

BlackScreaminMachine

iTrader: (17)

I heard bout the different sizes, but had not had the chance to tear stuff out. all good info.