The GT motor in a '69 (correct me if i'm wrong) would be a std block either 681 or 691 casting with the go faster add ons the 711 came out in '70 according to the Burton power site (
http://www.burtonpower.co...flow-tuning-guide.html )
if you get a Kent block you should be able to use the bits out of your old motor. I have 2 681 bare blocks and a 691 complete motor that needs work but I am probably to far away, having said that the blocks are common, 711 being the most sort after and also available new.