First question is this a British gun with 2 1/2 chambers? If so what are the proof marks? If American Id expect a 2 9/16 or 2 3/4 chamber. Define your gun so people can estimate what pressures it was designed for.
If British there is no 1 1/2 ounce load which would be safe. Zero. Nor a 1 3/8 or 1 1/4 ounce load. I would stick to 1 ounce loads tops in a 2 1/2, 16. Just because you might find a single load does not mean it will be kind to the gun and stock.
As to altering wads that is a bad idea unless you send six shells out for pressure testing. Taking away the Crush section, to create extra space, will alter both chamber pressure and cause more shot deformation at setback. If the load tests safe pressure wise, you then need to pattern it to see if it is worth using.
