Any recommendations for building a '73 340?

I'd use the 587 heads with the 1.88 intake valves. I'd only run the 2.02 intakes if the 1.88's are sunk too far in the head, the exhaust seats are already hard by 1973. Pocket port them yourself, just clean up the sharp edges under the valve. Use the crank from the 273 with pistons to get you to around 9.0 to one. Stock 273 Commando and 340 pistons are all cast. Use the 340 rods and have them reconditioned with good rod bolts and length equalized. Have the rotating assy balanced, and bore and hone the block with torque plates. Use good rings, see the thread on gapless rings. It is simpler to use the good Viton valve seals with single springs, which will limit lift and hp, but will last longer on a street engine. You will have plenty of power with a good 340 and 4 speed. On an early A body there are tricks and expense to running a 10.5 or 10.95 clutch. Check out Passon Performance or Brewers Performance. Have to agree with RRR about headers and Pishta about the pilot bushing in the crankshaft. I doubt you will need to stroke a 340, if you want a stroker just get a 360, and say goodbye to a high rpm screamer. If done right, your biggest problem will be getting traction.