DX 1.8 Block Difference

Hi,
I have two 1.8 DX engine blocks, one has the two rear corner extended castings with locating dowels for the head gasket, the other block doesn't. The one with the dowels is the later numbered block.
Can anyone tell me roughly when the change was made by VW and how the gasket is lined up properly on the block without the dowels ?
Thanks

Since you are getting new head bolts,  they can't be re-used  Cut the heads off of 2 of them and dont screw then in all the way and you can use those as a guide.  

But personally I have never used anything other than being very careful and starting all my bolts by hand then tightening them down in sequence.  

I suppose I have done a few diesels and my cabby's so that is about 6 head gaskets on my diesel over 20 years, if I would of known that the Stud kits bit better I may have only needed 1 gasket for the Diesel.  But alas what did I do before the internet.  All 3 of my cabbies had new head gaskets when I changed them out for the 4-2 exhaust manifold and dual down pipe.

I can remember the last time I did a Head Gasket on my Diesel it took 3 hours start to finish with new belt and tensioner.  I think my last cabbie was done in about the same time.

Thanks for your reply, excellent advice regarding the head bolts, great idea.
Do you know when the change in non- locating dowel to dowel blocks took place roughly ?