Hey Pat,
What "the hulls" are we talking about?
NAMBA and IMPBA 1.667 Gas Scale Rules are different and require different measurements.
NAMBA:
All required measurements including the range you can be within, are listed in the 1.667 Scale NAMBA Master hull Roster for each Hull number ever built. NAMBA required that the boats meet measurements of Overall Length, Beam, Maximum Depth, After plane Length, and Tunnel Width. Engine specifications: G or GX Class engines from 15 to 31 cubic centimeters. Ref: Section 21,Page 3, C. Hull Specifications 9. The propeller drive dog may extend one drive dog length beyond transom.
IMPBA:
Only requires the measurements of: "All boats built to a scale of1.8" to 1'0" (1/6.667 scale) plus or minus10% of the beam and 5% of the length."
For your 8910 hull: 31' times 1.80 = 55.8" +/-5% would be within a range of 53 - 58.59" Length Overall. Beam of 14 1/2 feet times 1.80 = 26.1" +/- 1=% or 2.61" - within a range of 23.49 - 28.7".
"The drive dog must not extend beyond the transom unless the prototype's strut and/or drive dog did also." Photographic proof to prove.
"Engine must not exceed a maximum displacement of 31,00 cc utilizing a single gasoline fuel engine with spark ignition and must comply with all IMPBA LSG engine and noise rules"
Here is a specific line items from NAMBA 1.667 Master Hull Roster.
Hopefully this will show the specific differences between requirements of the two Sanctioning activities for 1.666 Gas Scale.
Hopefully my math was correct. CHEERS !!! Bob