273 time to 'fish or cut bait'...

Some corrections: Later 273's come with CAST cranks; the exact same ones as the 318's. '68 273 had cast cranks for sure and had the larger register (hole) in the back of the crank. Unless you have a crank part number, OP, we can't say for sure if it is cast or forged. But it doesn't matter; either will work FINE for your level of torque and HP desired.

ROCKERS: IIRC: Hipo 273's had adjustable rockers. Low 273's performance ones of ALL years had stamped rockers. Having the adjustables is nice.

Heads: Those look like the 2 BBL heads. PLEASE tell the machinist to HOLD, go back to the shop and look for the 7 digit head casting number, along one of the ports. It may be one of these castings PN's:
Mopar Casting Numbers
I agree with Yellow Rose; those look like open chambers and are likely to be the 675's used on 273's and 318s. With the head PN, a lot more actually GOOD info can be given to you.

CAM: Rock Auto is not your best friend for cams! We can do a TON better.

As for the suggestion on the 318 block. I agree but only if you get the right pistons. Your described application is going to need torque for those great 0-60 times (unless you want to rev the engine up to 3k each time you want to depart quickly from a stop light or stop sign), and open chamber heads with stock 318 pistons don't get you there. Either the domed Egge 273 pistons (L2222) or some KB's in a 318 block are the way to go. Then you can keep the compression up for good low RPM torque AND keep your fuel economy up too.

Stock pistons won't work in bored cylinders. No way.