First off, let's assume we're talking about US market cars, in which case the chronology is quite a bit different from what you describe:

The B20B came out in 1969. It had twin carbs and 10.5 compression, and was rated at 125HP SAE gross. It was used until the end of the 1972 model year.

The B20E came out in 1970 (in the 1800E) and was also used in 1971. It had, compared to the B, larger valves and improved porting, as well as the D Jetronic injection. These engines used a D cam. They were rated at 130HP SAE gross. As far as stock engines are concerned, this is the one to have.

In 1972, the E was superseded by the F. The B20F (72-73) had slightly lower compression, a different head with more restrictive porting, and minor modifications to the D Jet system. These engines still had the D cam and 6 bolt crank. They were rated 125 HP, and are also good ones to work with.

The 1974 model year is when the major changes took place. The engine was still designated B20F, but very little remained the same about it. This is where the 8 bolt crank came in, as well as hardened valve seats. Also, all the threads in the block were changed to metric. Previous versions had been SAE. The 74s had K Jetronic (CIS) fuel injection, and to go with it, a K cam. Compression was reduced still further. 74 was not a good year. These were the engines with the porous blocks and wear-prone camshafts. I refer to 74 as "the year of round cams and oval cylinders" In my opinion, they are best avoided, except that the head is a quick, easy way to get hardened seats, if you can find one.

The 75 is pretty much identical to the 74, but with most of the quality control issues resolved.

To answer the original question, if I were looking to build a carbureted performance street engine, I would look for any 6 bolt bottom end in good condition, and top it with, ideally, a 71 E head (with the injector ports plugged) or, as those are very difficult to find, a 72 or later F head, perhaps with a bit of port work to bring it up (more or less) to E spec. Don't go too high with your compression--10.5:1 is a reasonable upper limit.

As for the camshaft, I have often heard that not all D cams were created equal, and that those in the 70-71 Es were more equal than the others, but have never seen any kind of official confirmation of this.