[papajam]

It is a 2L block, and I assume the 00526 means it came out of a super,...

Yes, the type 00526 engine was indeed fitted to the Giulia Supers but in 1600cc form, not 2L. The letter 'S' in the engine number designates an 'EmCon' engine (emission control) which, as far as I can determine, started appearing late 72/early 73. There should also be the letter 'A' somewhere on the front of the head.

 

[papajam]

Is there any chance they could have made 0526 engines in 2L?

Well, we are talking Alfa here. But I don't think so. The documents I have show that the type 526 engine is a 1600 thru 1976. And Alfa typically kept the displacement the same for a given engine type.
The '20' on the head, I think, does not refer to a 2.0l but is rather a casting number of some sort. The 2.0 casting on 2l heads I've seen is also much larger than whats on your head. Another clue is the square on the head. This is Alfa's symbol for a 1600. (see this post)
Another way to determine engine size is the distance from the top of the waterpump to the top of the block (the deck). On a 1300, the pump is about flush with the deck, 1600s have the deck about 25mm above the pump and on a 1750/2000 engine, the distance is about 40mm.

 

[papajam]

01629 engines were fitted to the 1975 & 1976 USA Alfettas as well as the 75-77 USA Spiders. Can't get any closer as I have no listings on a 9 prefixed sequential serial number (only 0 & 5 prefixes).

 

[papajam]

According to the list, there were 995 1970 spiders built for the US market. I have been given a lot of grief for saying I had a 70 spider by people who say there werent any. WHY?

Simply because there were no 1970 model year USA Spiders. The Roundtails built in 1970 were sold as 1969 model year vehicles. So your 10562 Roundtail is a 1969. The build year is irrelevant.