I'm one of the folks that has posted a few times the Ford manual stated the newer returnless 3L 4V injectors were 21lbs. This even as recently as last week or so IIRC. There was also a big post about it quite a while ago started by a NECO member. (he posted a scan from the manual but I don't know what year or model)
I've had no problems with tuning mine (from an 02 Taurus) and have my injector slopes at 24/28. My final A/F is nearly identical to what I am commanding with the fuel tables. Of course I have the cat temp switch off and a couple other "fuel" nannies.
I don't see anything wrong with running 21lb injectors on a 3L because you are never going to max their potential Normally Aspirated. However I do agree you need to know what size they are to program for them.
