I used a TCI Street Fighter torque converter with the same specs in my 4L80e and it was driven without an issue on the street for years. Prior to that I used a Corvette TH400 (non'lock up) converter (because everyone said a lock-up won't work), but didn't like the performance. The Corvette converter had a 2,400 RPM stall speed.
The lock-up feature only broke once when I was running some really sticky 14x33 inch slicks. TCI gave me a brand new converter under warranty without a question asked (maybe with a name of Street Fighter they suspect the car it is installed in is used for more than running to the store for milk and beer).
As to the lock up speed that is the point at which if the wheels do not rotate the engine will stall (hence the name stall speed). Your wheels will rotate on the street and aside from your tach bouncing up rapidly on leaving a stop sign you won't even know you have a higher than stock converter installed. You will need to install the biggest transmission oil cooler you can find to keep from burning up the tranny though as a loose converter generates a lot more heat. I used two 10,000 GVW tranny coolers in series on my car to verify it was chilling the fluid. Here is a product similar to the one I used:
By the way no one can predict accurately the stall speed unless they know the engine (cam mostly as the torque generated is the biggest factor, gearing, and weight of the total vehicle including a trailer if towing). Those figures are a guestimate.
As they say at the bottom of your EPA sticker your mileage may vary because it always does.
Which Holley EFI did you try the TBI self learning unit, or the 550-500 race ready version with port injection and is fully programmable?
As to tall valve covers I can not tell you if they will interfere or not as I have never put a BBC in that year vehicle with tall valve covers.