I'm building a 300 I6 and on other forums it was mentioned that 390 pistons will work in the 300 I6. They have the correct rod pin size of .9752 and are 4.050 bore size. The problem is finding the part number for a forged flat top 390 slug. TRW was said to be good and affordable, but what part number? Does anyone have a part number or any suggestions? I have learned a LOT by reading this site and fordsix.com, and cannot wait to get my 27 T HiBoy on the road!