Ian, you seem extremely reluctant to do this checking yourself for some reason. Go ahead and get the 20 degree heads and check them yourself. At the worst, you may have to use an Isky tool to re-cut the valve reliefs a little in the pistons. No big deal.
No matter what answers you get from others, if you don't check YOUR stuff YOURSELF, you won't have a definitive answer. There are simply too many variables between motors to say whether one guy or another had or didn't have clearance problems. Possible differences are as follows...
Block deck height difference
Rod center to center difference
Piston compression height difference
Block deck to valve seat dimension difference
Rocker arm ratio difference
Camshaft timing events difference
Here's a tutorial from Isky to help you check the clearance properly. Hope this helps.
http://www.iskycams.com/camshaft.php
You can rent the piston notching tool for US$40.
http://www.iskycams.com/onlinecatalog.html