To answer the op's question i have the 440 source heads , i took them to my machinist and he also was very impressed with the look and feel of the heads .
I had him do a valve job because i know that his performace valve job produces more power than stock . This is on every head he has done for me the way he does the back cut on the valves and the angles he uses is actualy like a 5 angle type valve job so on the Dyno they flow better .
I also had him install viton valve seals correct the valve guides and set a new set of comp cams Bee hive springs with 10 deg locks only because my cam go,s over 500in lift .
He told me that I would be pushing the envalope if I did not change to ten deg locks because my cam is aggressive ramp rates and more lift then stock .
If your motor is completely stock and you want to run them i am sure you will be fine and enjoy them .
they have to be better than worn stock 906 heads with the normal 1/4 inch of valve guide wear .
Like the others have said for 50-60 dollars i would up grade to some
comp cams or crane cam locks and keepers or at least the keepers so i could sleep better knowing that when i drop[ the hammer on cruise night (to show off )that my motor does not blow up all over the street as i do my burn out to go home after the cruise nite show !