I'm new to chevy motor tinkering my question is I have a 89 to 94 block according to the casting numbers. Can I use the "old" style heads on this block?  

You sure can.  

No problem with using older heads on the newer blocks, unless the heads are off a 400 small block.

The only thing you have to watch out for, some of the early heads have no accessory bolt holes, so if you're running accessories with early heads, you've got problems, or can't in some cases.  

thanks guys I took the heads off yesterday because I was getting water in the oil four of the head bolts were loose I had guys telling me it was because the older heads wouldn't work. but since i have taken it apart and seen that everything lines up problem solved. Is the only differnce the four intake bolts in the middle older at an angle,newer straight in? The exhaust manifolds even bolt up.