I bet its milled >400 thou. Run a tape across the china wall where it intersects the head and the intake, both my 273 and 360 measure very close to 7.5 inches. If its milled this will be <7.5. did you mention rod length? Those BME rods can be custom made to any length as the big end has a lot of room to offset. Even the little end looks to be forged long and they drill it to final length. View attachment 1715804382
Pishta, if I'm understanding correctly the dimension across the intake manifold valley, between the two head lands, I measured as 6.848". So considerable milling, consistent with the work done on the manifold? Seems like way too much.
The rod length is a little harder to estimate with the piston still assembled. I used a straight edge to extend the rod mating surface parallel to the wrist pin and measured to my eyeballed center of the wrist pin and got a measure of ~6.075" The rod mating surface is serrated, so I assume the actual measuring surface would be at half the tooth depth. Unfortunately, the BME receipt I have doesn't have any part no. details.
I have the original receipts from Brooks Racing Components (BRC) which calls out the piston as 10-1-55-251. Google says that the current shop RaceTec (in Huntington Beach) is the second generation of BRC so I thought maybe they could decode the number and give me some piston dimensions. They're pretty close to you, do you know anybody there?