When I was researching my impending motor swap (later model Mustang, essentially same engine), I used google HEAVILY. There may be swap motor mounts available, but the tubular K-member is absolutely the best way to go (if it's available). Check BMR or AJE. If anyone has one, one or both of those companies will.
Next, if you're going to make more than 350-400HP, you're going to need to upgrade your transmission. I think a Tremec T56 Magnum may work for you (if it fits in the trans tunnel). If the Magnum doesn't fit, a TKO 600 will be your best bet. You'll twist a T5 in half with a stout 351w.
The next thing you have to concern yourself with is electrical stuff. If you want to keep your OEM instrumentation, you probably have to retain the ECU. Want A/C? more electrical stuff. BTW, I'm using Fox body accessory brackets, an alternator from a 94 Mustang, and a A/C compressor from a 93 Fox.
Finally, you have to concern yourself with hood clearance. A 351 with an OEM EFI setup is going to be TALL.
I would send the motor you have to a machine shop to be rebuilt - there's no point in putting in a used motor without knowing what's in it (or wrong with it). Also, put aluminum heads on it. A 351w with aluminum heads weighs less than a 289/302 with iron heads.
If I were you, I'd budget $15k for this swap.