my 1st 340....yea

69 340 would have 894 X heads and just not worth the $ to put them on. Stupid money for essentially the same thing that you have in the 915 heads, other than the X instead of O, J letter etc. 340 Springs if they test good are fine for most mild hyd cams for a streeter

You have a good base of parts to get a OEM style build together. Balancer is a internal balance piece as Randy (1Wild) mentioned, hopefully the crank matches.

No need for the flywheel to balance an internal set up, except to check the actual flywheel balance job. Buy a neutral balance flywheel for a 4 speed, done