interesting! the .090" was for a 225 so your going to have to CC the chamber, figure out how far below deck the piston is then figure out your current and future compression using this
cylinders: 6 bore: is 3.400 unless its been bored (measure when head is off) stroke: is 3.125" for 170 Head CC's: (stock were around 53-58 but you more worried about final CC's) Valve relief/dome: (stock) 0 Gasket thickness and bore: (stock was 3.400 by .021 thick compressed) (most aftermarket ones are 3.510 bore by .021 (steel) or .037 (felpro) so you need to get it in hand before milling) Deck height: with the piston at TDC you will measure to see how far down in the hole the piston is. but it looks like stock 170's are zero decked
so stock your probably at a 8.5 or so, I would recommend about a 9.2-5 compression, but what is your octane there?