BT's great pic above confirms that the crank is a cast one. (Look at the "parting line" running from the crank pin up towards the main bearing - see that is it rounded, and not ground on, as a forged crank would be.)
As for a stroker "kit", Falicone cranks emailed me that they can do a welded stroker on your Bonny crank. Even though it is a cast crank, an expert welder should have no problem building up the botton side of the rod journal (probably with an intended-for-cast-iron nickel alloy arc rod).
To make it easy to get the proper piston, just get a set of custom Carillos which are shorter by half of the increased stroke. In other words, if you stroke it by 10mms, get a rod that is shorter by 5mms. Then you can use the stock piston pin location (known as "compression height").
Wow, an 1140cc Bonny motor! South Bay must be using their machined-from-a-solid-chunk barrels along with a stroker crank. Sounds good to me!
