i'm interested in building a 427 for my 66 caprice I have a steel crank truck rods tall block rectangle closed chamber heads. I know this can be done with a short block but I have to buy pistons anyway and already have a 4 bolt tall block, will this work or should I keep looking?  

A tall deck block for a performance rig makes little sense to me, and a set of closed chamber rectangular port heads are worthy of being thrown in the trash and that's it.

If you were to build a straight 427 out of a tall deck then you would need to add an aftermarket, longer than stock length connecting rod just to find an off the shelf forged piston to work. In tall deck form the compression distance of a piston for a 3.76" stroke and a 6.135" rod would be over 2.0", which isn't easy to find.

Adding aftermarket rods to a GM crank with aftermarket forged pistons doesn't make a lot of sense economically either.

Maybe if you built a 525 (that some people were talking about earlier) out of this tall deck you could actually use a rectangular port with a healthy solid roller, but then you're still being held back by a poor combustion chamber that is shrouding the valves. If you put a rectangular port on a 427 you might as well be building a 350.  

With passenger 427 pistons you'll need .400" longer rods the difference between 9.8 to 10.2 deck heights.If this tall one can fit in the engine bay,take advantage by making a 4.25 crank 6.535 or 6.700 rod 489-496 stroker or the above mentioned 4.50 stroke 525!      WIEDER