There is lot of mis information about handling issues with an extended fork and big angle of the neck. And if the wrong geometry is employed a bike handling can become dangerous. The main issue that is often overlooked that if addressed properly is the trail measurement. If the trail is in an acceptable range the length of tubes and degree of rake becomes less of an issue. The Spoiler front end is an example where the bottom of the fork moves the trail measurement to an acceptable place and the bike handles fine. I have seen 10 foot plus wheelbase custom choppers without wheel flop. It is not just the length of the fork its all about trail. You can google a host of info on this issue along with various calculators to determine trail. Here is a site that has a good explanation of the geometry and a calculator.
RB Racing Rake and Trail Calculator