I'm new to all of this but very curious of the possibility of putting in a new engine in a fastback but with the new engine being close to the original? Are there any other good engine companies that make specifically for these mustangs?  

Any small block Ford will fit in the '67. Either something 302 based or 351W based will be dead simple to put in. If you want a big-block FE or such, you might have issues with the shock towers and headers.

The only big concern is whether to go carbureted or fuel injected. Obviously a carb setup is much easier, but the fuel injected setup can have better fuel mileage as well as less maintenance or adjustments needed after its setup and installed.

Check out this article from June 2005's issues to get an idea of the engine choices out there.

http://www.mustangmonthly.com/techarticles/mump_0605_ford_small_crate_engine_guide  

The way you asked your question tells me you're new to this and money may be an issue.
Check out articles on "crate engines" and stick to the 303/5.0 engines.  Fuel injection costs a LOT more than a carburator setup.
Read the tech articles on this website and subscribe to some Mustang magazines.  

bE CAREFUL WITH THE 351 WINDSOR.....IT IS VERY CLOSE TO THE SAME BLOCK AS A 302 OR A 289 BUT WILL SIT HIGHER AND YOU ARE LIMITED TO WHAT INTAKE AND CARBURATOR YOU CAN USE OR YOU WON'T BE ABLE TO CLOSE THE HOOD....  

There's a huge selection of crate engines at JEGS.com
If you're looking at the FORD 302 with "Z" alum. heads
mustangsunlimited.com has the same crate engines for
less money.
Good Luck,  MB  

Edelbrock does make some crate engines but from what I have seen they only make chevy's. They do however make top end kits for engines which include cam, lifters, heads intake manifold and carb which are pretty nice. You could get a short block and dress it with Edelbrock components all matched to each other. Ebay is another good source for crate engines. Search "302 engine" and you will find some good buys on there also.