Yes, you will have to add lots of weight back in! Stock 340 pistons are 719 grams with a 154 gram pin....
The H405CP is what I would go for... Ooops...one problem; they don't have pin lock grooves in them. Probably the same for the Silvolites. Sorry to not see that before.
Back to something like the ICON FHR 9975 to keep the CR down below 9.0. 606 grams with 118 gram pin. These are forged, but I agree, forged is not necessary for this build level.