First of all, if you think that you will be able to properly rebuild your motor for cheap, then you may as well look for a used, running type 4/bus motor and slap that in.
Personally, I would not even attempt to rebuild 30+ year old heads that have most likely have detonation damage, cracks in the exhaust ports, and dropped (or incipient) valve seats. Get a new set of AMC castings prepped by Len Hoffman -
www.haminc.biz.
If you are going to do the rebuilding yourself, i suggest you get a hold of the Bug Me videos Type 4 rebuild dvd.
Also check out the type 4 forum on shoptalkforums.com, and Raby's site at forums.aircooledtechnology.com. There is a wealth of information on the Type 4 motor and bus applications there.
Good luck!