Worth it to build my 273?

High 12's is ambitious for any engine. I recently read that the 1/4 mile times for the top-line factory 340 A-bodies were ~13.5 sec back in the day. That was with factory bias tires. I think to get there, you will need wide drag tires, perhaps requiring tubbed rear wheel wells, and a stronger rear end (8-1/4 or 8-3/4) and maybe a custom tranny. Of course, now you are getting to a drag-only toy, not a daily driver. There is more pride in going fast in a 273. Some guys are in the 11's with a slant six, but not cheaply (turbo, etc).