I have a 4.3 Chevy 1500 trans went bad got one at junkyard but it comes out of a ls motor mine is vortec I can’t find any kind of adapter kit ir anything or if I even need anything to make it work ? The torque converter holes are a little wider than the flex plate holes. What can I do to make this work.

 

There is an adapter kit available which is basically a spacer for the entire bellhousing; IIRC is cost over $300. There are additional complexities with the torque converter; might need a new one.
Frankly you simply bought the wrong transmission; take it back (ort sell it) and get the correct one.

 

They is an adapter from LT small block to LS motor is a sleeve for the converter, However going from the LS trans to the 4.3 is not something I think they make an adapter for, The converter pilot for the LS is simply to long, Now I did once see a guy grind it down to fit and amazingly it did work but I do not suggest this.
As mrvedit says you have the wrong trans best bet take it back and get right one.
Other options = change out pump, input drum, bell and converter, However at that point may as well rebuild the original for the time , effort and money involved,

 

Frank, there actually is an adapter made by GM, it is part # 19154766 and comes with a new flexplate too. However it is quite pricey as Summit lists it for $470, although someone claims to have it in stock for $340.
It is described as "Adapts transmission and torque converter for Gen 3/4 LS engines to Gen I and Gen II-style one-piece rear main seal small blocks."
I don't know if a 300mm converter will then fit with it or not.

 

Cool I was unaware of it. So now I know. but yes that is a bit pricey Particularly if the goal is to install a used trans with it. Which IMO a USED 60E unless you know it was built and when and what is a bit like USED CORN if you know what I mean lol.