Old No7 :
Yes the bolt pattern on the 401 is the same as the 305, so any of the V6 bellhousings will bolt to the other V6's. Only thing to look for on the bellhousing is if it is for the small trucks or the big trucks. Depends on what the engines came out of but the big truck bell housing won't fit in a pick up. Here's what the small truck bellhousing should look like:
http://www.ebay.com/itm/1966-1967-19...r#ht_641wt_674
If you are interested in these motors, a wealth of knowledge resides over here:
http://6066gmcclub.com/forum/index.php
Hope this is helpful.
regards,
Steve
New Orleans