commando cam .. how much will it take with stock specs ?

You have to measure lobe lift against your rocker ratio. (1.5 vs 1.6)
Fyi, we put a Comp 270S cam in our 273 with 2bl pistons. 0.468 valve lift 0.313 lobe lift. Sounded great, ran "great" but was a dog. Put Ld4b on it, I did a diy redneck port cleanup. Didn't make much of a difference.
I've started to build another Small block to transplant.
IMO Commando pistons account for a lot of the 273 potential. Limited mfg for the pistons out there. When I knew I wanted more hp, I knew the 273 was going to cost me more $$ per hp gain than other sb choices. Look at the engineering it took to get the D-Dart to 275 HP. A lot.
Just an fyi, good luck whatever route you choose.