i believe dark greens (803's) begin to struggle at around 380+ so should be fine for 350.

if you wanted more than 350bhp then you could also look at using light blues (403's) before the greys (400's)

as for pistons they don't generally come in a specific comp ratio, you have to get the piston crown machined the the desired ratio that you require.

give paul at pj motorsport a call (01902 862882) he'll give you a good price.

paul