ive had this for years came from western s.d. Block cast number is 1238861. Vin on both is 42z117519 wf on deck 72bs on the trans tag and short ext housing. I don't see bs in my books for t400 code? In a gs? Also have the heads gregg I checked the production numbers of 72 this fits 1 of 1099 gs 455s 1 of 44 gsx s or 1 of 126 verts! Also z is Fremont gregg
BS is a correct code TH400 for a GS455 and possibly a Stage 1 in 1971 (even though the BB and OW are listed as correct). There is a grey area or an odd car that is an exception to the rule. It isn't as common as the BA but it is listed in both the service manual and it the Ron Sessions book on TH400's.
