Welcomne to the Stovebolt!
If you poke around in the Tech Tips area of this web site I think you'll find a discussion of putting a GMC 302 in a Chevy pickup. The 270 and 302 are basically identical on the outside, so what you read there is correct for this swap too.
Basically the 270 should bolt to the bellhousing just fine.
The question about using the GMC bellhousing is more compicated. What year is it? '54 or later and the answer is different than if its '47 to '53. The issue is that the crossmember changed in '54.
You also have potential issues related to the foot starter if you are swapping to a motor that was 12-volt.
