Deploying Win7 to 3 dell models using one reference computer

Hi, first post here (long time lurker) .. I was unable to find the best answer for my senario, so I started this thread in hopes someone else will be able to use the solution as well.

At my work place, we are going to deploy Windows 7 to about 20+ computers. I am familiar with WinPE, sysprep , and imagex , but what I am
not sure about is drivers for the 3 different models of dell computers I will be deploying to.

Models of computers are Dell Optiplex 755 , 760 , 780

Do I have to capture an image from each model and put all three images into one wim , then say imagex apply index # for the respective model?

Another idea I had was to custom build a Win7 install usb (see below)

Make a bootable Windows 7 USB stick for install, but replace the install.wim with the .wim from my reference computer (will this even work?)

Then using DISM , inject ALL drivers say \drivers\755 , \drivers\760 , and \drivers\780 to the install.wim or boot.wim (not sure which one) so
when the installer runs, it finds the neccessary drivers for the model I am installing to.

Does this make sense or am I way off here? In the end, I want to deploy to all 3 models with sysprep'd image from a nicely configured reference
computer.

Thanks for your help!!