need some help for a newbie.

i am looking at buying a a833 for a 71 340 manual car that i am picking up, but i cannot find info about the differences in the regular and the od trans.
the guy says that it is a a833 out of a duster, but how can i be sure?
he wants 350 for it, and says that it is good. is that too much?
he is also selling me his 340 that has a casting date of 9-69. it is completley apart. has every thing for it except the x- heads that he sold already. is there anything on that block that i should look for as in damaged areas? he also has a 440 b/b sitting with it, and now i need to go through all the internals and other parts to find out what i get with it. i dont want to grab a balancer for a b/b for the 340...
on the inner side of one of the balancers, it looks to have a section that has a weight on it. it is molded into the metal. it is not a seperate peice, but that is the only way i can explain it.
am i getting robbed for 800.00? i just want to do a stock rebuild on it. the crank looks to be really good, but i will send it out to get it polished when i get the rest of the engine work done.
please give me some feedback guys.. oh, and i cannot figure out what waterpump is the right one either, they both look to be about the same:angry7: