A few notes:
It should be noted while generally all the Force 22 cranksets have removable spiders, not all the Red cranksets do. In particular, the Red Exogram cranksets have one piece crankarm-spiders.
If your frame uses a braze-on front derailleur, you may not be able to get the derailleur low enough to shift a 42-28. However, you might be able to get the derailleur lower with a
WickWerks Fit-Link, which allows the front derailleur to be mounted up to 2 cm lower.
Depending on derailleur shape, you may have an issue with clearance between crankarm inner face and the derailleur cage out plate. Because the crank arm is angled outward from spindle to pedal, there is less clearance between chainrings and crank arm as the chainrings get smaller. Both chainrings are mounted to the inner face of the 120/80 crank spider, so you may get more room by installing chainring spacers, to offset the chainrings inward. This will also have the affect of reducing the chainline offset. The outer 120 mm BCD chainrings are held by bolts that thread directly into the chainring, so you may need longer bolts to accommodate the thickness of the chainring spacers.
Longer 120mm BCD bolts are also available from WickWerks.
Since this gets into the territory beyond which the crank/derailleur was originally designed to work, the results may or may not be satisfactory. I've gotten a Campagnolo shifter/derailleur to work adequately with a 44-29 crankset, but I've never tried the combination you're suggesting. My experience with 42 and 38 outer chainrings has thus far only been on the stand in the work shop. It seemed to work, but I haven't tried shifting under load yet.