Hi Julian, from the Pegasus site....
"Boots for 94mm OD Lobro CV Joints (78mm Bolt Circle)
The Aero boot (shown at left in photograph) has no convolutions and is much more aerodynamic than bellows-style boots. The Standard bellows-style boot (shown at right) is much more flexible than the Aero boot. The Aero boot has a maximum angle of approximately 6 degrees. Both types fit our 94mm OD Lobro-style CV joints (Part Nos. 1471 and 1473). The bolt circle diameter is 78mm."
Given that most GT40s already have some amount of CV axle offset due to (typically) rearward positioning of the transaxle output flanges relative to the uprights, six percent maximum working angle isn't a lot.