Any recommendations for building a '73 340?

you want a high revving V8 and are ditching a 273? 73 340 was a cast crank, weird balancer, weighted convertor...I'd take the advice and build it to a neutral balance mill. Then you can use neutral balanced rotating parts, flywheel and balancer. Youll need to machine the crank for a manual pilot bearing/bushing or use the 273 manual crank and balance job.