Sorry. I didn't notice you said impact gun. I use a half inch drive Dewalt drill motor. It doesn't have the hammer effect like an impact gun and it works fine.

I was only spin starting a little LS3 100. Doubt I could do it on a 250 but maybe if it had an automatic chainsaw style decomp in the spare plug hole it might work. Anyway I probably tighten my mag nut to twice recommended-- but I'd better not recommend that lol. Have done it on my 360 with plug out just testing spark. Think I was strobing the timing at kick start speed  come to think, & made easy work of it. I saw a random video once with someone starting a bike with a flywheel using a belt around the flywheel & around his scooter rear wheel minus the tyre. Or did I dream that haha.

If it has good compression and it's not firing with starter fluid you're not getting good spark at the right time, full stop. That's why two strokes are so nice to work on! Fueling is an issue (or not) that can be sorted after it fires/runs on starter fluid.

"I saw a random video once with someone starting a bike with a flywheel using a belt around the flywheel & around his scooter rear wheel minus the tyre."

You didn't dream it. Snowmobiles came with a webbing strap for wrapping the primary clutch to start them when the pull cord broke, have had to do it myself, on a 900cc twin. Thankfully the clutch is pretty big so it gives a good ratio for pulling.

Like Schu I've seen it done with a drill too!