Hi Fred,
I'm planning on fitting a 3.6 with a tiptronic gearbox from a 1995ish 993 Porsche in to my 71 baywindow.
Having spoken to a few people who have done these conversions before they recommend the earlier engines, however the 2.7 is not a very reliable engine (again this is what I've been told) so it's a difficult choice to make, perhaps you might want to speak to your local Porsche specialist as he will be looking after older cars and should therefore know their weekness's
Basically if you want a more reliable engine you will need a newer one but this will make it more difficult to fit.
I'm not too sure if I've helped much here
Rob.