Any engine can crank walk. Most 4g63 engines that were going to already have. The 420a in stock form won't handle much power. The compression is too high, you might squeeze out stock gst hp out of it without blowing it first pull. Chances are it wwon't last long either way. Now, with a properly...
Bad or too small of a ground is what immediately came to mind when I saw this. It should have a ground from negative post to firewall, negative post to bell housing, and intake manifold to firewall. Check to verify if these are still there, and if so, if they're in good condition, I.e. not burnt
Try hooking that ground back up. I'm no expert, but it could be the ground for the heater circuit in the o2 sensor. The sensor itself has its own ecu ground. If that doesn't work, it could be a faulty sensor
And really, a 20g wheel with the tdo5h turbine isn't going to be a jump big enough to warrant buying it. You'll still be limited by that turbine. Jump up to a tdo6 variant at the very least. That e316g wheel is already enough to overrun its turbine.
You have to use the turbo mas. Mine did the exact same thing. My stock mas had been hacked, so I decided to use one of the nt mas' I had. I had to swap back to get it to run right.
You have to modify the 7 bolt mount bracket to fit past the water pump. But I'd stay away from JDM engine importers. You can usually find low mileage built engines for less than what they want for a stock engine in unknown condition.
Just a silly question, but covering all bases here. When the turbo swap was done, you did use the turbo fuel pump, mas, ecu, and injector resistor pack, correct?