Hey bark, good luck with the build! Here's my 2c...
1) Not sure about the head configuration, but I would tend to also agree that for a forced induction application, the money could definitely be spent better elsewhere. I'm sure an efficient turbo will be able easily compensate for any meager flow improvements a bit of porting could offer.
2) Later B6 DOHC 16v (mid to late 90's) may also have been fitted from the factory with a laminated steel head gasket like the BP's, from memory, but it's been a while. Whilst in a lot of turbo applications there is often no discernable difference in the appearance of a forced vs normalliy aspirated HG, they may very well differ in actual construction and composition (and hence genuine/aftermarket part number). Forced inductions HG's must cope with much higher cobustion pressures and temps.
It important to remember that there are several variants of the B6's, so ensure you specify as close as you can to the actual build date when ordering it, otherwise I can guarantee it will be wrong (or bits of it, anyway). If I was building an engine and designing it for high boost, I would certainly do my best to find a HG suited for that app, even if I was forced to purchase it separately to the full gasket set.
3) Don't worry about a thicker gasket! These are pointless for this application and generally designed for applications where excess material has been removed from the head or block during any machining processes, or where pistons protrude from the block at TDC (as in many diesels and very high compression race applications). Highly boosted turbo cars built around thick HG's, head shims or decompression plates are just asking for trouble IMHO. There is no compensation for lower compression pistons, especially when you have the thing apart anyway
Also, most ACL gasket sets for later model south east asian or european vehicles will have been imported and repackaged by ACL from manufactureres such as Payen and Ajusa, it is just not cost effective for them to manufacture them. This can actually be a very good thing as a lot of the time they can be far more complete than ACL sets!
I'd try and locate an Ajusa set, personally, as i was always impressed at the completeness of their sets. I also used to have one of their gasket catalogues, and it was by far and away the best catalogue of any vendor I had ever used (seven years in that industry). Companies such as Veale Auto Parts over here in WA can help you out with Ajusa.
4) I'll happily be the eighth or so person to mention ARP studs and bolts, definitely a good investment!
Lower compression pistons are of course a must (compared to NA). Exaclty what compression you choose is the question, and will probably be determined by your budget. Either you grab the B6T pistons and suffer the relatively poor off-boost performance, or you fork out the bucks for the alternatives that offer you a better choice, Wiseco, etc. Also make sure the pistons you choose are matched to your rods, or alternatively, make sure you get rods to suit whatever pistons you decide upon. This is important as most turbo engines will also use shorter rods in order to maintain or increase crown thickness on the turbo piston. If you use unmatched pistons and rods, you may not achieve your target compression ratio.
Also, if you are having the block and/or head faced (and you definitely should at leaast have the head faced), make sure you know what type of HG you have decided on, as it technically should effect the finish that the reconditioner decides upon (ie a different finish is required for composite vs steel HG's). Of course it is equally important that you find a reconditioner that knows this and will machine it correctly, as many don't/won't!
While you have the engine apart, also consider ancilliaries such as the water pump, timing belt and tensioners, harmonic balancer, etc. It's easier to replace these now, rather than later!
Cheers!
