First of all, WELCOME TO CFF!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Those look to be medium bore carbs. The good ones! I know you are going to the closed deck block for more power and dependability now. Are those 30 or 31 series seizcos, I mean wiseco's???? The first 2 numbers of the part number tell the series. the 30 series are absolute junk!!!! The 31 had some improvement and were alot better. Now they have 32 series with a total design change and have only seen them for a few engines. I don't use wiseco's, but for the engines you are looking to build, persans are my choice!
It is hard to tell from the picture but the hole in the piston indicate extream heat and part of the piston is gone and this looks to be on the portion facing the exhaust port. The damage on top is probably from the piston melting and having no ring grove, broke a piece of ring off. This is caused from lean fuel condition or a power pack double firing. A double firing pack will ignite the plug twice per cycle at different times and burns off all the residual fuel that sqelches a cylinder keeping it cool. I find a ton of these on Mercury's. You will have to install the pack on a running engine to test the power pack for double firing. This is a fairly simple task with timing light and a dial indicator to be precise but are other methodes to find out. That is why I replace the packs on almost every rebuild. It is easy to repair the damage but you have to take steps to prevent it from occuring again in a short amount of time which is what this one looks and sound to have done. Are they the same cylinders again? Hope this helps!
