Did a Google and found this but have no idea of any differences. This guy was changing from the five bolt housing to the six bolt
Dave
The following part numbers are of aluminium 6-bolt bell housings which you can use with the 10 1/2" clutch:
C5DA - 6394 - A
D20A - 6394 - AA
D5DA - 6394 - AB (swap clutch arm pivot from old 5-bolt bell housing)
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427R Roush-with Roush 540 motor,2300 TVS
'66' Ranchero w/almost done 302 T-5 swap
2005 4x4 Ranger
2001 Ranger Edge
'69' Fairlane Cobra, 428 4-speed waiting for work