If you do be sure to get a big block heater core in there before the motor,it will be easier and you need to have one if you want a heater.
The hose connection on a small block core ends up behind the big block head when you install a big block so it can't be hooked up,ask me how I know, lol

 

The core itself is different on a big block Y2Keglide?
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Thanks for that

 

Yes,the small block and big block are different,on a big block the hose connections are outboard towards the fender to clear the bigger engine.

Small Block:


Big Block: