The .241 should be safe for a cast piston. Its the .161 that is going to be kinda' on the fence. How big of an area is it that thin. Now that the tops have been cut, how far down is the top ring. Keep in mind the 366 piston and wrist pin are a whole lot heavier than the stock 292 piston and wrist pin. That will potentially put much more stress on a rod that wasn't engineered for that extra mass hanging on the end of it. So be cautious about RPM, as the piston speed of the 292 will be much higher than the 366 at the same RPM. Just curious, did you check the weight difference between them.
