If you can get Cleveland heads for $50-$75 a pair, it could be worth it. The last Ebay auction I saw, the heads started at $250 or so. That makes it much less attractive.
Do check out
http://www.pricemotorsport.com/ if you have any interest at all in Cleveland engines. They have adapter plates to mate an EFI intake manifold to Cleveland heads or Cleveland heads and block.
The heads will need to have hardened valve seats installed to be used with unleaded fuel. That adds $275-$400 to the cost. Then you need adapters to mate your EFI manifold to the Cleveland heads - see
http://www.pricemotorsport.com/ for the adapters. The 2V adapters are $255, the 4v adapters are $267. If you use the 4V heads, you need a set of port stuffers to reduce the port volume in increase the flow velocity - that adds $112 plus maybe $150 worth of machine work to install the stuffers. Then you need to modify the heads and block to make the water passages line up. New push rods and gaskets are needed too.
Totals: ( I’m sure that I have missed some things)
2 V Heads
$75 heads
$350 machine work
$225 manifold adapters
$650
If you paid $350 for the heads, that works out to $1000, and a good set of used Trick Flows or AFRs could be had for that price
4V heads
$75 heads
$350 machine work valve seats
$267 manifold adapters
$112 port stuffers
$150 port stuffer machine work
$924
If you paid $350 for the heads, that works out to $1274, which is close to the price range for a new set of AFR's
If you have to change the pistons, this isn't a bargain. If you can run the 2V heads and stock pistons (don't know if this is possible), it could be a cheap upgrade.