This would be what I would do, keeping a budget in mind.
Check out the explorer engine, if the compression is good and it does not have a ton of miles I would yank the heads, and get a set of aluminum heads, nothing fancy, a voodoo cam for that classic idle and good low end torque, duel plain intake (nothing fancy, they all make about the same hp and torque) a 650 cfm carb, long tube headers and full exhaust. A 355 gear in a 8.8.
now if I am interested to spanking your buddies bmw then I'm gonna need a turbo. More work, bigger budget.
Now I will park that mustang in a parking lot car show next to that bmw and watch people gather around my stang, they will point at the bmw and whisper as they walk by but gather at my car and talk.
so the choice is yours, budget build that has you cruising for years or a bmw spanking, money pit that did not come with jack stands.
I'm am not against turbos, they can be a reliable very fun way lay waste to rear tires and embarrass many newer cars but it come with a price. And I have not even begun on the brakes,
suspension and other stuff that needs attention when building a car. Any car.