I'm considering this on my 225 build, but it presents a question...pins! Are the pin sizes of the 2.2 turbo pistons and the 198 rods compatible? Or is some machining needed here? And what 2.2 pistons are commonly used? I've heard that 1964-69 Corvair pistons work as well.
Thanks!
________
Arizona dispensaries

The 2.2 pistons have the same wrist pin size as the SL6. (.901)
You do need to check clearances base on the exact 2.2 piston you end-up with because some are slightly smaller for a "floating" pin.

This is the main reason this "long rod" swap is so popular, it all "bolts together" with-out any special machining and there are a number of different 2.2 pistions styles to choose from, ranging from a large dish turbo piston, a mid-size dish & even a flat top piston... basically you can get compression numbers between 7.5 to 11 to 1 when swapping them into a SL6... just by doing the math and careful piston selection.
There are a lot of the 2.2 family (87.5 mm thru 89 mm) pistons still in distribution but most of the forged ones have "dried-up".
(TRW / FM / Sealed Power list old P/Ns)

As for the Corvair piston, it works... I have used those but availability is limited these days. (no off-the-shelf forged pistons anymore)
These pistons use the Chebby .927 wrist pin size so a SL6 con rod will need to be reworked to fit.
One more thing, those Covair pistons start at 3.500 bore and they have a pretty slender "slipper skirt"... so when using these pistons in a high HP SL6, I have had the same broken piston skirt "illness" that many GM hot rodders seem to get.
DD

Thanks for the reply Doc. Wow, that doesn't look good, so I guess I'll forget about the Corvair stuff!

So if I wanted to end up with perhaps a 9.5 CR with a piston that is zero decked (maybe half dished?) in a stock bore, is there anything specific out there to look for with the stock pin size?

Good decision, the 2.2 piston "family" is the place to look for low cost (cast) long rod pistons.
Do you have a set of 198 (7.005 c to c) connecting rods?
If not... start looking... those are not real easy to find.

As for the 2.2 pistons, all start at 87.5 mm (3.445) so you need to do a .045 overbore to a factory bore (3.40) SL6 to get a "standard" 2.2 piston to fit.
After that, there, many oversizes to choose from. (88mm, 88.25. 88.5, 88.75 & 89mm are offered)

ebag usually has a number of listings, this one shows the "medium dish" version that is commonly used in a mild performance (street on pump gas) SL6.
Using this piston, with a 58 cc head (factory) and "clean-up cut" block deck, a mild cam (Erson RDP RV10/295) gets you a 9.15 static C/R and a 8.0 DCR.
Run more C/R if you want more to run more cam. Do the DCR calculations.
I have built many of these engines... they run well.
DD

Good info, and I saved it all!