Technically, yes.. you could get domed pistons.. or drop the liners and run mercury pistons in the bare bore.. and perhaps relieve your head a little to allow for valve clearance then shave it for comp ratio... however.. the gains are very small.
There has been negligible discusion on mini-superchargers.. etc.. but again.. the gains are diminishing compaired to the cash outlay.
I believe someone here on the list has used the following phrases:
" nothing better than cubic inches at souping up an engine than cubic cash"
and my favorite:
" How fast is your wallet "
In the end, you can sink enough money into an 8n engine to get it up perhaps 6 or so HP.. and nearly double the cost of the thing... Better bet if ya want 33 hp is to sell the 8n and then get a naa or 600 series tractor that has an OHV 134ci engine vs that flatty l head of 119ci that don't breathe good.
You could also move up to an 800 with a 172ci engine in the same package size as the 134.
Or.. if ya like the 8n look.. you can get v6 and v8 conversions and repower it.
All are spendy ways to get hp.. except for just buying a tractor with the HP you want.. etc..