Carb suggestion for a 512 with trickflow 270's

A Holley Sniper would solve a lot of problems but you would need to come up the learning curve on EFI. The Sniper is fairly easy to install and you'll get data logging as a bonus. If you want to stick with a carb then most any of the larger 4150 carbs should work. A 850 or 950 or even 1050 will work. The smaller ones will work better on the street while the bigger ones will make a little more power at the track. Personally I'd stay on the small size with the carb if this is your first engine build. The smaller carb has a better chance of working out of the box.