I am in the process of putting together a stroker 340 and ran into the exact same dilemma. Originally I had purchased flat top pistons however, I ended up returning them for dish pistons. After all of the machine work to the block was completed and prior to returning the piston, I considered trying to make it work with using a thicker head gasket, enlarging the head chambers, tulip valves, and milling the pistons.
I came to the conclusion that the dish pistons would be fine for my application (street motor, w/hyd cam) I was okay with the lower compression.

Is all of your machine work done to the block? Have you checked the specs of other piston manufacturers? The other option are custom piston.

Good luck....