In what way are they different ? A/C , water pump , power steering , alternator , crankshaft ? they can't be all different . I have pulleys and brackets for both early and late big blocks . Yes , they look different but the function is the same . Let me know what diameter pulleys you need and what the offset is and how many grooves in the crank pulley and how many grooves in the alternator pulley and maybe I can help you . Or you can take the whole water pump housing , water pump and brackets etc., etc. from another BB and see if it lines up . I can help you there also . I think 400's have a longer snout on the balancer but I'm not sure .