bc broncos has some cool stuff and will help explain some issues with the intake.
their adapter to put the mustang intake on the 351 lower is pretty cool...used to only be 108 bux shipped...not sure what it is now as the prices arent on the page till you order from what it looked like to me.
http://www.bcbroncos.com/fuelefi.html
i mod the upper framerails a bit and you can use sn platform or fox swap type 351 headers, most units clear with aerostar linkage and factory box location.
with sas, if you go with a over rail type steering box and build a nice k member you can fit about anything you want. i have seen a few trucks running eb headers using similar setups to the horn mounts i have made before. i almost used that setup initially when i swapped the 6.5 into my rig when i pulled the 302 out. its easy to do and tie together with channel and makes pulling the oil pan for inspections a breeze.
most guys just trim the stock ttb member with sas trucks and thats fine for 302's and stock engines, but beyond that, building a nice k setup is ideal and opens up so many more options for steering and headers and oilpans and shit like that..
you can fit a stock 351 efi setup with a 3 in bodylift with custom k member...or horn/k members.
but honestly unless your building horsepower as a initial goal, a stock mustang setup on one of those bc bronco adapters is the easy button and you get a much nicer torque curve over a 302. run the mustang cam with a rollmaster timing set and i could be happy with a rig like yours.
if for some reason you want to make some decent power, you will need to go to a different setup all the way around anyway so living with a stock efi 351 is a great way to get started really....
i have extra stock ho intakes laying around if you want to try that route via the bc bronco adapter as well. active military guy would get that for the cost of shipping from me. been injured and laid off or i would just send it. but my wife will kick me in the balls if i do.
you plan to run the stock electronics as well?