The part numbers, stamped on the side of the block above the breather box,
which pertain to the 1800E and B20E engine are 496940 to 496949.
Any B20 short block will work but you probably want one with a "D" cam.
Later B20F models (which will also be functionally identical and have the
"D" cam) include 498038-498049, 498052-498063, 498066-67, 498190-91,
498222-23, 498268-498289, etc.
In the above numbers, the digits 4969 or 49 will be cast on the side of the
block while the remaining digits will be stamped on a boss next to the cast
numbers.

If you are willing to replace the cam, any old B20 short block will be fine.
The 8-bolt block will require different bolts to mount the bellhousing.
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George Downs Bartlesville, Heart of the USA!

Short block usually means that they don't come with a head installed on them, so it'd just be the block. A long block usually means a block and head together. I'm currently selling what I would call a long block on ebay right now... B20s aren't really model specific unless you want to keep the car with the same motor it had stock, then there are other designations that come into play, such as b20A, b20B, b20E, b20F and so on. Your 71 1800E probably came with a high compression FI b20E. But you can put almost any b20 you want into the car to replace the one it came with. Although, the b20E is the highest STOCK output version of the b20 available. Hope this helps!
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Kyle - VP of OVT Membership - www.OVTuners.org Portland/Corvallis, OR - 1968 142 - current setup: 71b20b SUs, m40, bigger list available upon request... ;)