Lawmakers and experts reviewing a proposed bill that seeks to drastically overhaul the secondary mortgage market without the need for Fannie Mae and Freddie Mac question whether the Federal Housing Finance Agency is the most appropriate choice to implement key components of the program.The Private Mortgage Market Investment Act, drafted but not yet filed by Rep. Scott Garrett, R-NJ, would create a heavily regulated mortgage-backed securities market made up solely of private entities that would function with no federal guarantee at all.