What is the easiest way to build a post sample SCAR 17?

Do you have access to a manual mill?

Easiest would be to get a complete factory select-fire lower and then run an end mill across the top so it'll fit the semi-auto receiver.

Then swap for a select-fire bolt carrier, or add a weld to the existing carrier to gain a sear trip.

That's what I remember from when my shop converted one anyway. I might be a little rusty, but I don't recall there being anything in the receiver to deny the auto bolt carrier.

Thank you for the info.
Do you have any idea where I could find a select fire lower? I am having trouble coming up with one.

You're welcome.

I hardly ever see them offered for sale.
I'd start by trying FN directly.

Then MGW: https://www.midwestgunworks.com/fn-scar/complete-trigger-module.html
(They list FN's part numbers here.)

Then finally maybe hi-desertdog.com (call them) but they'll be sky high, and may only offer their in-house aluminum version.

Last time I saw their select-fire SCAR 17 bolt carrier, it was just a formerly semi-auto one they welded up themselves. (They didn't explain that in their description either.)

You might be able to buy another aftermarket aluminum version and convert it instead. (Never seen that in person though.)

If you call Geissele they may sell you their select-fire version of the Super SCAR hammer & trigger. (The regular one is not compatible.)

Did someone say SCAR auto bolts?
https://www.admmfg.com/scar-bolt-carrier