FYI: -The N-Series Cylinder Head used a stud and hex nut until mid-8N production and then switched to just a hex head bolt. The head has 18 holes with 15 being the same and 3 being deeper. The switch to the hex head bolts made it so one size was used on all 18 holes. Torque specs differ for the 7/16-20 hex nuts used with the studs and the 7/16-14 x 2-3/8 Hex Head Bolts. JUST8Ns offers just the bolt 'like original' at $5 each. STEINERS offers the 7/16x 3" STUD at $4.50 each. I found better sources for the studs and hex nuts -see LINKs below that are perfect and the price is good at about $31.80 for 20 studs, $39 with shipping. The length is 3", more than the OEM, but you can grind down the ends to match. MPC lists 15 at 2.78"L and 3 listed at 2.9" L. Caution is advised to ensure the thread length isn't too short or too long. You do not want the stud to bottom out on the non-threaded shoulder nor not have enough thread for the nut. The OEM hex nuts have an 11/16" AF dimension too with a 7/16" thickness. I could not find any hex bolts like the original other than the ones Just8Ns sells at $5 per bolt, specially made with 11/16 AF hex head and length at 2-3/8”. McMaster-Carr sells a 7/16-20 Hex Nut, Grade 9, exact of original with 11/16" AF and 7/16" thickness. For the costs involved, I'd opt for the studs and hex nuts. Total 20 STUDS = $39.00 + 20 Hex Nuts at $15.76 per 20 pcs, shipping extra. I also found another source for the 7/16 x 3" studs at Mid-States Bolts -p/n 9732.
OEM style hex nuts: https://www.mcmaster.com/95036a037