The race preped boss 429's were one of the badest mustangs of all time and there were only a few with the nascar engine. The regular street version wasn't so great. Remember reading tests on them in hot rod and so fourth back in the day and they were a little disapointing. They were nose heavy and down on power for a 429 hemie. However, there were a few let out on the street with the race hemie and race preped that were to die for. If I remember correctly, it was less than 20 of the good ones, they had a different letter in thier code. At the time ford had to produce 500 of them for the street in order to race them in NASCAR. Don't remember what the actual production numbers were, but it was low and some were better than others. However it was all for not as NASCAR outlawed the hemie from competison. No one thinks about it, but ford had 2 hemies, the boss 429 and the 427 sohc create engine, dodge wasn't the only one.