The last year or so of B18 blocks were externally like early

B20 blocks, with the reinforcement bracket and extra holes and

lugs to mount things. I suspect that they may also have thicker

cylinder walls but don't know this for sure. The one you got is

probably B18 B or D from 67 or earlier. I haven't seen one with

a temp sender hole, but you should be able to put the pan from

one on the other.

Remember the B20 has a bigger bore. If you put a B18 head on

a B20 you will get higher compression (but smaller valves

and ports, etc, so it's not a good deal).

B20Es had 10.5 which is probably all you want. B20 and B18

cranks and rods are enough alike to be pretty much interchangeable,

and the rods and pistons are the same length. Different models of

B20 had different thickness of head to vary compression and also

in the later models, thicker gaskets to lower it. The fuel injection

heads also had bigger valves. For quite a few reasons, if you can

get a B20 E or F, you are better off to change the whole engine,

and if you get an F, you may want to mill the head to B20E thickness.