Want to put a new very powerful engine in a 67' Mustang. What would be the best and most powerful engine I could put in without doing a ton of fab work?  

See what you think about these guys.  They build Race engines but also street engines.

http://www.tandlengines.com/Street_Engines/Ford/ford.html  

Do you know anyone who has engines from these guys and what did they think because they look legit?  

Forget the fab work, the least expensive horsepower that fits and works reliably is right from Ford.  The 392 Stroker (based on the 351) has great torque and power but torque is what counts from stoplight to stoplight.
I did and use a TCI built C-4 with 3:55 gears.
It works great.  

I agree with PeterDaPan - go with one of the many stroker crate engines, from 347 to 427. Your '67 will hold a big-block, so a 351W based engine will definitely fit.

Donald Farr
Editor  

I have a 67 fastback with a 351W.  It has a somewhat taller deck than a 302, so is an easy fit.  Great power with much less weight and obviously an easier fit than a big block.  You can really get good power with a good intake and carb.  Mine has a mild cam and a good electronic ignition.  Also have an non-electronic AOD with a lockup torque converter.  It is really fun to drive.  The rear end is geared pretty high but it still has good power.  

351 Cleveland