One set up that trumps all others for the 250 is the adaption of the EFI 4.9 serpentine drive.All power options with room for headers,air pump, a/c, p/s, tensioner and no water pump, just and idler where a reverse water pump might have been.
http://repairguide.autozone.com/znetrgs ... 0723c9.gif
On f150forum.com, the EFI set up comprises just a passenger side low mount air pump, then 3G alternator, tensioner, drivers side Ps and an A/C unit which was optional. There is a common EF and EL Falcon balancer which allows the whole set up to blend into a US 200, or the stock 4.9 balancer for the 250.
The pictures are from page 3 and 4 of the above forum
http://www.f150forum.com/f13/fuel-injec ... 11/index3/
http://www.f150forum.com/f13/fuel-injec ... 11/index4/
The water pump can be eliminated, and replaced with an EWP Davis Craig set up, and an idler gear added where the water pump was. Balldrick, CYCO250 from Xford forums, and our and73greenmachine have done it.
Takes a bit of nutting out, but the parts are perfect for our small sixes as well as the 240/300
The other thing is that the 250 Classic Inlines engine and head combination
73GreenMachine has made is perfect for an F150 4.9 EFI throttle body, eliminating the hood clearance issues all the 250 engines have in cars with shallows hoods (especially the Mustang 68-73 X-shells and Fox body Fords).
The serpentine drive would be the icing on the cake.