I am replaying FO1 with a stealth character.

Now I'm in Junktown trying to finish the assassination for Gizmo.

I'm nowhere near combat ready enough to just stroll into Killians store blasting away. I've tried planting grenades on him, but they don't go off. I've planted dynamite on him and had it detonate, but then he doesn't have the dog tags (vaporized by the blast?).

Anyone out there have a solution to deep 6 killian without having to shoot it out with all the guards?

As fair as I know there is no other way. You can try at night, when he's alone in his room. This would give you more time to recover having killed him. The dogtags, if I recall, are in his safe... aren't they? It's been a while.
Which companions do you have?
Dogmeat, Ian (Without an SMG) and Tycho are great help in battle. You can have all three at that point in the game. Ian in Shady Sands, Dogmeat and Tycho in Junktown.

Just blow him up in his private room at night. Sneak and use some dynamite. I'll have to agree with Cliffworms on the tags, I think they're in his safe. If they're not, try killing him with ordinary weapons, using sneak again, and check his not blown up corpse for the tags.

I'm sure the tags are on the corpse.

On a lark I tried the dynamite again.

I don't know what went wrong the first cupple of times, but after running around to the rear of Darkwater's, I was treated to the planted explosives death animation.
Checking the corpse, I was delighted to find the dog tags this time... and the icing, none of the guards reacted at all.
Thanks all for the help...