I have and still am looking at F engines for my lakester. I've mostly considered ones with good potential blown. With that in mind one of my first picks (and these are considering motors that are affordable) are:
First choice might be the Toyota JZ engines....
http://en.wikipedia.org/wiki/Toyota_JZ_engine6 cylinders lots of main bearings and people are making big reliable HP with these engines. These were hard to find, but are now coming in from Japan as they are coming out of cars over there.
Since I'm kind of a Chevy guy one I'm also leaning towards is the baby to what Sparky has there and that is the I-4 GM used in the Colorado/Canyon pickups. He has the 6 cylinder that was used in the Trailblazer. The I-4 and I-5 are just shorter less cylinders of the Trailblazer 6. The 6 fits right in the top of the E motor class and the I-4 is right at the top of the F motor class.
People are making a fairly easy 1500 HP with the 6 so 900-1000 with the 4 should be very doable. They all use the same pistons/rods/ valve train and so forth just different cylinder count. The stock heads flow very close to 300 cfm and with just a little work will flow about 330 cfm. The exhaust side needs the most work as GM limited that side for emissions (what I've read). They are running the 6's over 10,000 na but I'd shoot for about 7500 blown. The drive train can cost a lot for the high rev limit as this is a DOHC motor with 4 valves per cylinder so you start to buy a lot of valve train components with the 6 and with the 4 about the same amount as a standard V-8.
They don't have the older GM bolt pattern for the bell housing but Sparky and I just bought adapters that allow older stuff to mount to the back of the motor. They are about $200.
Not much out there on these motors but here is the best source I've found and I have more links if you want them....
http://www.vortec4200.com/forum1/.. the site is mostly 6 owners but almost everything applies to the 4 cylinder also.
I'll be interested in seeing what others recommend,
Sum