That is a lot of head for the cubic inches you are talking…
Not to chg your mind but why the M heads vs the 351 Windsor which should give you approx 35 hp with new pistons ?
What will this engine be doing and what RPMs will it be running ?
What is the valve sizes in the “M” Heads ?
Remember the first Boss 302 had 2.19” intakes and it was too much valve for the street, racing it was great the Boss took on a lot and beat most of them.
Sorry for all of the questions, I am going to pull my old For dPower Kit Books and see what Ford suggested for this “M” Swap.
4x4, 5sp, Std Cab, Stepside, E4 Red
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31 Spline FX4 Rear Axle, 4.56s and OX Locker, Hurst Shifter w/Optional Stick and "Made by Grev" alignment adapter