The 307 is a good engine to hot rod and responds well to typical hot rod upgrades.
Like cam, compression ,, valve size, head port flow,, induction and exhaust system upgrades.
But increasing the bore size in of it self will not add power in any meaningfull way.
If you are going to bore it for new pistons then do that for that purpose.
As said get better heads for your 307. ALL the stock 307 motor heads suck.
So lots of good choices there.
check the cylinder head casting number, between the valve springs on your 307 heads.
What other SBC heads do you got kicking around? (casting numbers)