Proibe Phil you can't compare webers to holley carbs,for JHV48 it doesn't matter how many motors he built, bought, or leased. Weber carbs are great for CERTAIN applications. They make great MIDRANGE HP. 48mm where used for the 289 motors and could rev them to 7,400 rpm. They had the on the GT-40's but opped out of the single 4 barrel. A lot less moving parts for a 24 hour race. Less things to break, come loose, or fall apart. This is an endurance race, not a 4 hour speed race. There also had a 6,500 rpm limit on the motors to save them for the 24 hours. They gave up 35 HP in the midrange with the holley but picked up top end speed. I never saw a set of 58mm on a 289 motor. The 58mm Olbergs and Webbers where for the Can-am cars. I asked you to send me a copy of the specs from your motor, I received nothing. So here goes, You want to run webers, run them, The cam is large but the webers will remove some of the lift and duration if they are setup right. 11.0-1 compression is OK. The CFM is going to be the limit on the motors rpm. In the high rpm it's like you trying to suck air through a straw. The motor A/F is going to richen up from no more air flow. 48mm Have a limited rpm in a 427 motor. It's about max CFM of the carbs. The only differents is you are running 8 carbs instead of a single 4 barrel carb with a min of 650cfm air avaliable for each cylinder not 280. KCR has a nice smaller roller camshaft for your setup. RUN IT. I have one of his cams,roller for my 498 motor with 58mm TWM setup going on it. Yes I have alot more drivablity then you will with the webers because of the computor and other sensors. Even before CC started guys where running webers on 427 motors, and they all say just about the same thing, Great midrange power, proven on the dynos, both motor and chassic. Problem air flow at high rpms, the little carbs run out. If you have and real port work done to your heads, they are going to outflow the carbs. If the webers where so great, everyone would be running them at the race tracks, They only ran the 58mm for the 427 and up motors. I hope you are running an air box that is pressurized. Reason the back carbs DON'T get the same clean air as the front ones. Air also doesn't like to do 90 degree turns. The only BBC motors I have seen and running well had on the 58mm Olbergs or Webers. Small blocks, I have seen alot running the 48mm setups. Your money, time and car, Do what you want, If the motor has a melt down, build another.
Bigger is not always better, that's all the guys on the thread are trying to say and save you alot of money and problems.
Yes I learned the hard way too.
Rick L.