1978 T/A 6.6 engine questions:
What block casting is the correct one for this engine?  Did it have 6X heads? What Pontiac cam came in it?
I just got a pair of '78 T/A's, a keeper and a parts car.  The keeper was bought engine disassembled with most of the engine parts with the car.  I have 6X heads, and the block is missing the main caps--I know, it is nearly useless w/o them, but I also have the complete, running 6.6 Liter engine out of the parts car. It too has 6X heads.  I thought the T/A 6.6 had different heads from the 6.6 Liter.  I know the donor motor has not been into, nor any parts swapped on/off it.
According to the letters I got from PHD, the T/A 6.6 had fatter jetting, a different cam, the Pontiac 350ci heads, and chrome valve covers, and that by the VIN, I have a T/A 6.6 car. I know those 350 heads are rare today, if what I've got is actually four heads for the weaker motor.  

Yes, the TA6.6 heads using the 350 heads which means higher compression than the regular 6.6 heads.  To verify which 6X heads you have, look for "4" stamped on the boss up near the valve cover rail.  Those are 6X-4 which are higher compression.  The stock heads should be stamped "8", IIRC.

The cam is also different, but not that much.  When I put my 79 TA6.6 back together, I used Summit K2801 cam instead, which works with all the stock valve train components (use new lifters, of course).

You can always reject the QJet, of course.  I recommand keeping it in any case.  

You can go to Hitman's T/A webpage were there's a link to John Witzke's W-72 history article. All the info you could ever want on this engine package!

http://www.78ta.com/HTMLobj-16215/W72TECH06.pdf

Best of luck!

Kevin