Based on what you all have seen, which small blocks have:
1. the thickest main bearing saddles/webbing? (In a magazine article linked on this site there was an older 318 being built up and it looked like it could be fitted with 4 bolt mains!?)
They are all identical in the main webbing areas. As was said, only the TA block had enough meat added for 4bolt mains, so adding them to any production block weakens the webbing overall.
2. the thickest cylinder walls? (I think someone already voiced their opinion on an '89 LA 360 block.)
It's a misnomer. Mopar had blocks they wanted to be thick. Those in LAs were the early 360s (71 cast only) Some earlier 318 blocks have thick walls too. But the only way to know for sure is to sonic test. If your shop doesnt have one and know how to use it then go somewhere else. Two of the thickest blocks I've ever tested are the '89LA 360 I'm working on now and a '73 340 block I did two years ago.
3. the most consistent wall thickness or least core shift? (Later blocks because of machining improvements?)
The later blocks seem to be the best for core quality. But the iron is not as thick overall (better castings=less iron needed). The best bet is an earlier block with no shift. Again, this cannot be seen without sonic testing.
4. the stoutest cam valley? (Did chrysler ever make sb without those huge windows in the cam webbing?)
No. And IMO there's no reason to. They dont split there very often. Most blocks you see with the covered cam tunnel is for oil control (windage) not strength.
or is there a book on all this stuff I should pick up?
There are a bunch, but some of them have the same misleading info in them. So I'd say buy anything that catches your eye, read them all, and research things. One of my best books is oil soaked and dog eared and I bought it in 1986. The latest book (Szylagi's.. sorry for the name butchering) is good, but like many leans too heavy on MP parts and leaves some things out.
Thanks