Seriously?

The first thing you say to your customers is: Year, Make, Model, Engine, 2wd or 4 wd before you can help them.

Also you do know that a good many "Rebuilt" parts are all crap right outta the box right?

Unbelievable!

 

brand new not reman. And no thats not the forst thing you say😂😂

 

Whew !

You might try these 2 things to narrow down the problem. Please don't kill yourself in the process.
1)sometime when it won't crank, without moving or disturbing anything, try the screwdriver/solenoid trick and see if it cranks.
2) (this takes 2 people or some jumpers for your volt meter) when it doesn't crank ,without moving or disturbing anything.see if you get 12v at the appropriate starter terminal( see service manual) when you turn key to "start"

Depending on how things go you should have a better idea where to look for the fault.
Again...be careful

 

If the starter is new, then you might want to check your battery cables and grounds.. Cables can have hidden corrosion underneath the insulation and grounds need to be removed and cleaned. Most notorious gremlins of starting issues. Also the adjustment of the neutral safety switch is in play since you have had an engine swap.

 

How did you verify it's not the NSS? Seems like you've done minimal testing, like seeing if you're getting a signal to the starter solenoid.

 

.

.