The A12 from a Datsun 1200 [1970 to '73] will physicly bolt straight into the 1000, but the stock aircleaner usually rubs on the underside of the bonnet. A factory GX intake system fits wonderfully, but you need the oval intake port head to use it.
If you use an A14 head, it will need a small mod to allow the oil to reach the rockers as the engines from '74 were diferent.

The 1200 gearbox will also bolt straight in, but you will need the 1200 clutch cable & you need to make an adapter to mount the 1200 cable at the firewall. You may also need to do some "creative masaging" of the trans tunnel to clear the clutch arm. It's all less difficult than it sounds.

It's good to see that you are stepping up. Welcome to the exclusive 1000 group.