I checked out the Hum3D model and it seems pretty good in most areas.
The overall length of the limousine from the WC/HSCA was at-or-near 255" (42.6" longer than a stock 1961 Continental). On this model, it's 248" (35.6" longer than a stock 1961 Continental). The light projections on the front bumper would add another 2 1/2" to the model's length (making it 250.5"). But we don't know what two points on the car were measured in 1963/64 or if the official figure was measured on an horizontal.
There's a researcher named Roy L. Schaeffer who claims the limousine is 248" long. I think the foremost point of the front bumper and the rearmost point on the rear bumper are obvious places to measure between (as I have done with the model).
The wheel rims are supposed to be 15" wide but the model shows 17" (the Hess & Eisenhardt profile photo supports the smaller rim diameter; maybe the rim in the model was one used after the "Quick Fix" alterations and is currently on the limousine on display at the Henry Ford). The rubber tire reportedly was 27", so 26.5" on the model is very good.
The rear door on the model measures about 40" long on the outside. The door seam tapers at the rear top of the door, so the door length reduces to 38" for the inside. The glass opening in the partition on the model being 9 1/2" wide seems correct. The curvature of the parade bar feels off; the bar doesn't exist in the limousine on display as the car was given a permanent roof. If the limousine on display was scanned, they would have to approximate from photos the parade bar.
The door handles and the chrome script reading "Continental" were reported eight inches long each. I have added onto the rear deck some figures from the WH/HSCA diagram.
Most impressive is the approximately 78.6" limousine width, the published width for a stock 1961 Continental. We don't know what two points were used to obtained the width (door handles and the projections along the wheel wheels are a bit outside the car's "slab sides". On this model, there's a very close correlation of the official car width with the width on the model between the "slab sides".
I would feel more confident about this model if the overall length issue (255"
vs. 248") was resolved.