(Newbe) 273 to a 340 and tremec 5speed swap.

For a "Newbie" you seem insistent on biting off more than you can chew, coming up with elaborate swap ideas for the most work and fab imaginable in your efforts to do a cheap flip. Just get a 318, a crank flange bushing for your pre-'68 transmission, bolt it in and sell it. Other than the flange bushing, it's a straight-up "unbolt the old and bolt in the new" swap; no parts chasing, fab or custom work. Done.