I must strongly advise *against* installing this kit in a basic A1200D case.
The heat generated, in conjunction with the current load (assuming you are powering it via the normal connector) will be well above the design ratings for the 1200.
Phase5 didn't reccomend tower installation for nothing. The basic BVision card alone runs *very* hot, hotter than any other expansion you will have ever come across. Every Permedia2 card I saw for the PC uses a heatsink on the chip.
Then you have an 040 and PPC, both of which dissipate more heat than a desktop can reliably cope with (without additional cooling).
Unless you want to run with the case open, or with an absurd number of small fans all around the inside, additional powerfeeds into the unit, etc, I'd say forget it and go for a tower.
-edit-
About performance. Depending on what you are accustomed to, the 040 will run OS3.x very well, especially with a graphics card. Of course an 060 is even better.
If you are running OS3.9, the picture.datatype supports PPC for colour remapping and dithering. Coupled with PPC datatypes for common image formats, you'll be really surprised at the speed increase in multiview, wbpattern preferences (and anyhing else that uses the picture datatype).
For example, on a 28MHz 040, a 1024x768 jpeg can take up to 40 seconds to decode, quantize and dither for a 16-bit display.
Expect about 2-3 seconds when using a good PPC jpeg datatype (WarpDT are excellent) in conjunction with 3.9's picture datatype.
