A suggestion if you think you might start installing "frame mounting" type racks as a part time hobby business.
One of my early customers is also now frame-mounting GEBE kits, so he and I are cutting the steel blanks 20 at a time, enough for 10 bikes, pre-drilling that top centered hole the engine mount attaches to.
This would be the same advise for Staton or any other frame-mounting possibilities.
And I mentioned how we are now sandwiching a rubber gasket in this thread:
http://motorbicycling.com/showthread.php?t=2099
If you think you are going to build more for your family and friends, start making steel drilling jigs of the 2 holes above the axle slot where they attach.
In other words, if you get a Wally World bike, or a Schwinn, or a Sun, etc, when you get those bottom holes lined up perfectly, make 3 copies, 2 for that bike and one to keep for future use when another identical bike shows up on your porch.
Basically, you save quite a bit of time if you repeat success.
Between us, we have now built up an "archive" of 6 different bottom hole alignments, and it makes it
SO MUCH EASIER if you have those jigs available, for the next time you see the same bike.
(I finished one antique Raleigh bike where the gap between the holes exceeded the width of my steel blanks, so I had to buy wider 3 foot piece of steel, durnit. But at least I have a jig if it ever shows up again...
never )
I also had a carpenter take one of Denis' perfectly centered wheels and make me 3 curved 8 inch wooden jigs, to slip in the space between the spoke ring and the wheel, so as I'm aligning the notches, I keep those wooden spacers in the gap to ensure even better ring centering.
I rode Jacks California Stretch Cruiser the other day, the one he claims tops out at 52mph, and instead of the GEBE supplied front strap, he bought a heavy gauge aluminum strip at the tractor supply, and I'm thinking about making that a permanent modification too.