All the protoform bodies have a square in the wheel location (dont know how else to explain it) you mark the center point of that square. Now there are two ways of doing it, you either do it by eye or do some markings on the body to try and center it up, you want the front drive shaft to line up with that making in the square ( for the front, the rear will line its self up more or less), check by feeling or measuring that the there is the same distance between the outer edge of each front and rear wheel . This will get the body centered. Now, if you want to get the posts lined up straight with the body, find an approximation point of both and draw a line of best fit across the bonnet and boot to go from (try draw this from somewhere you know is straight (eg edges of the wheel square) mark the holes, ream them( before or after painting it doesnt really matter) and then get some masking tape and cover the square from the inside of the body so you can see through it after painting (front AND REAR,). After painting mount the body and make any adjustments to the marking of where the drive shaft meets the box in the front, and also now mark the rear.
For the cutting of the wheel wells, youll neet a circular cutter, make the radius 68 mm, for the front, go 1mm down and 1mm back from the point, for the rear go 1mm down from the point.
Then score a line with the circle cutter and cut the peices out of the body with sciscors.
This ensures neer perfect body position with no wheel tucking since the cut out is round and contours the wheel nicely.
I wrote this in a bit of a rush, if I havent made anything clear enough just let me know.
Id be happy to post pics when I do my next shell.
I learnt this off someone when I was eager on getting a nicely mounted shell and wheel whells, just passing on the information.
Hope this helps!!
Also the idea is that once you know the holes arw neer right on one shell, if they are a little bit out, make small adjustments to the body hole positions on your next one. (Stick one shell inside the other and make markings) this saves time and improves consistency between shells. If YOU mount them the same every time then you willl have consistent handling in regards to your setup and the you will not have the issue of the body being a factor.