Have some number off the block want to make sure what this is. On the Block the number 3830830-1-400
and on the bottom of that there's another number
looks like a build date 12.3.74. Thanks for the help.

I don't know casting numbers but judging by that vacuum cannister, lack of casting pad beside the distributor and 2 barrel intake. I'd say it's a 400.
You are going to need a 400 harmonic balancer.

I gotta 440 crank thinkin about stroking it..My buddy who gave me the motor says it has a spun bearing haven't opened it up yet.

You sure about that casting #?

From the casting date I'd say it's a 75 400.

Should be a pad that is an extension of the deck surface in front of the passengers head (the books always say it's next to the distributor-but it's higher up in front of the blocks head surface). It is usually covered with crud you have to scrape off to see the stampings. If the number 400 is stamped on it, it's a 400. Mine has this pad, and I'm sure all 400's have it...., unless the deck surface has been milled down enough to erase it!

The last "400" of the casting numbers is the CID. A 440 would say 440, and so on.