If you can screw in T/C nipples snugly, seat the shoulder of the nipple against the breech, and pop a cap, seems like that would tell you the tube is long enough. Again, you would want to make sure the threads you're screwing into are still in good shape, but it sounds like you've already ascertained that.
The Track of the Wolf Catalog lists hot shot nipples, 'made of hardened stainless steel' and 'reputed to give better ignition with Pyrodex'. My experience with them was pretty short-lived. Twenty odd years ago I put one in a T/C Seneca, and the second shot fragmented a cap where I had to dig a fragment out of the web of my hand. I kinda lost interest in the 'Hot Shot Concept' at that time.
Ampco nipples claim to be more resistant to battering down or burnout than standard nipples.
I doubt it makes too much difference which you pick. I'd probably buy T/C standard nipples, and if I experienced ignition problems or unacceptably short nipple life, try Ampcos the next time around. Fortunately, nipples are pretty inexpensive.