Put # 092 heads on my stock 400 and need pistons. Can a flat top pistons work?

No, there 2 things to consider. First the valve pockets location and angle for the 1966 and earlier heads like the 092 have a 22 degree valve angle and all 400 (flat top) pistons have a 14 degree valve angle. Also you need a dish since the head cc is low (rated about 66-68cc). Once we dish the piston it would provide valve clearance. It would give you a compression ratio of about 11.0:1 which is way out of pump gas friendly range.

Here is the piston in dish version you would need.

https://butlerperformance.com/i-31644256-butler-ross-quick-ship-16-to-42cc-dish-top-forged-pistons-3-75-str-4-150-bore-set-8.html?ref=category:1394344

You can pick your own dish cc or we can choose one for you based on engine and head specs and your desired compression ratio. We recommend (9.5:1) on cast iron heads.