Fusion King,
Well since nobody else has helped, I will try. I checked the drawing for the block in question, and its cast from plain old 356, heat treated to the T-6 condition. So that means:
1-Preheat to 275 F for about an hour
2-Weld using 4043 filler and limit the amperage to about 200
3-Return to the oven for an additional hour after welding, then let it cool in the oven after turning it off.
This is a common practice to weld on 356 engine castings, done all the time on aircraft engines, and automotive. Good Luck!