I would not buy a cracked upper.
Nodak Spud or Nodak Spud via Brownells is your best bet for an authentic A1 upper and lower unless you go the gunbroker /gunshow route. Another option might be an Anderson etc... lower (cheaper than Nodak but not authentic A1 profile and the colors will not match) and a Nodak A1 upper. There are a few sources for the 20" barrel Delton,Green Mountain, Brownells. The furniture can be had Numrich, sarco and a few others. Lots of fun to build but beware quite addictive.