It's been done - Yella Terra seems to make the kit that's easiest to work with. I've weighed in on that thread in the last week or so, so it should be failry easy to find...
Now, if someoe offered roller lifters and a cam profile to match, I'd get one in a hot minute! Roller rockers are a "complement" mod - but roller lifters allow for much more aggressive cam lobe profiles, and for more "valve open" time than conventional "flat" tappets...
Hell, even "mushroom" tappets would offer room for improvement!
5-90