not sure on the balancer just yet but at first looks it looks like it should work.
as for the RB30's and how long they last, ive known of them doing up to 400,000k's and still been going strong.
mine has done 214,000 and the bores still look awesome. and im basically going to be doing exactly the same as you and throw the r33 rb25 head on the untouched rb30 bottom end and see how long it will last and the power i can get outa it. when it blows, if im happy with the power it makes and how long it lasted ill just get another $50 bottom end and start again.