Hi , I am no expert on the 383's , I had one that a previous owner put in a 70's blazer , It was supposed to be 10:25:1 compression with the comp cams 280 duration , 194 heads , 750 holley double pumper ,long tube headers , 2500 stall turbo 350 , 4:11 detroit locker , wide ass 50 series tires ...