I have the eb engine with motor mounts the manual 6 speed tranny with cross member the ecu the wire harness the rear end and driveshaft from a 2017 mustang what mods do I need to do to allow drop in and also is it possible to use the oe shift lever
There is no "drop in" with this swap. There's a single running example of a 4cyl ecoboost ranger. He started with the ideal swap chassis (an 01+ Duratec 2.3l/5spd) and he still had to chop up his firewall, cut out his heat/AC, ditch the power steering, buy the expensive Ford Racing controls pack and do a bunch of wiring. In an older truck like the 91 in your profile, you'd have at least that much to do, and probably more as its not even setup for OBDII. Plus you'd have to make engine mounts and nobody really knows how much clearance there is between the ecoboost oilpan and ibeam crossmember.
And getting it into the truck is the easy part. Then you either buy the expensive Ford Racing controls pack and get to wiring or if you're cheap and extremely knowledgable about CAN BUS networks you get to convince the CAN network that all of the different modules are there and happy. If neither of those is an option then you need literally everything electronic from the donor car. Just having the PCM isn't enough. We're talking entire wiring harness, gauge cluster, pedals, steering column, fuel system, and every module that controls things like lights and airbags to HVAC and stereo to tire pressure/stability control stuff.
Here's what a "drop in", turnkey kit for an ecoboost swap looks like:
That makes the Ford Racing Controls Pack seem worthwhile to me but maybe you're a better man than I am.
Oh, and the Mustang shifter is going to sit back quite a bit from the stock ranger shifter location. Things like T5 swaps moved the shifter back about a foot. I'm guessing it would be atleast that far with the Ecoboost trans from the current chassis cars.