Actually you are with in less than 3% what is advertised. Not being a Engine guru, I would say thats awsome with out spending allot of time making adjustments. My concern would be all the Tolerences that seem to be changed, we all know that adjusting this can rob some HP, if I had to guess that is what happened and once the motor is broke in you will see the 20hp, who knows maybe more??
Really hard to compare a stock 500efi/whipple set up to a 500efi/whipple set up not exactly stock. Cannot tell youhow many times changing something in a engine that should have made more power actually made no gain or less for no real reason???????
My 2 cents