Here's the deal...... 1981 ,  I need to do head work ( valve guides, etc.) on the engine .   I have access to  both 194 (aprox. 1970 date codes), and 2.02  GM  fuelie heads ( 1969 date codes ).  The 194's are ready to go,  the 202's are in good shape but may need to be freshend up.   If I do nothing else but change the heads ,  how much more performance  will I get, if any, from the 202's  vs.  194's  vs.  rebuilding the stock '81 heads ?

202s will help it breathe better, however, if you have the stock 1981 cam (mild lift) and exhaust manifolds, you may not see much of a noticable difference.

The casting numbers are more important than date codes.  Get the numbers from your current heads and both sets of replacements, and look on line for flow numbers.  If you are going to spend any money on repairs, you might look at new Vortec heads instead.  But Paul is right.  Your current cam is very mild, and I am not sure how restrictive '81 exhaust is.  If you are only going to do the heads, I would do whatever is most cost-effective.

Larry

If someone is trying to sell you some "fuelie" heads with '69 dates....yer gettin scammed. The last fuelies were made in '65.
Not to say they aren't the same castings, and valve sizes, but that in itself doesn't make them "fuelie" heads.
The valve sizes really won't make much noticeable difference on your engine, as Paul and Larry have said. If you do go with the 2.02 heads, tho, you'll be able to bump up the cam and pistons later on, and have some good heads to work with those mods.
If you don't plan on any major mods later on, then stick with the smaller valve heads...

Thanks guys !  good info .  

you'll probably also notice if they are smaller combustion chamber heads(which most likely they are being from 69-70 era) that you're compression will also go up a bit, along with the redline rpm... on dad's vette, before doing any mods to the engine, i had gotten a set of double hump heads with small valves, the 1.94.. the heads were 300 horse, 1966 date.. just a straight replacement of heads, with the stock heads(1976), i notice a considerable increase in the top end rpm(not to mention some more hp at the wheel)... best i recall(was like, 12-14 years ago) i gained about 1500 or more top rpm's... and, i'm sure it would still pull higher, i was just a bit timid about pushing any further... didnt have a back up vette at that time :)

I put on a set of 202 heads just for the better flow, ported/hogged them didn't really notice any performance differences though, if you do change keep your old number matching heads.