For thos that have done pourable transoms?

[THEFERMANATOR]

I'm in the process of doing a poured in transom for a boat I want to sell(boat is in great shape except somebody didn't seal up the transom cap). When you poured it what did you use to seal up the holes in the transom? This transom has a spot for a livewell pump in it, 2 drain plugs, and then the 4 engine mounting holes as well as some other various screw holes in it. Will some good commercial grade real duct tape do the trick? And lastly, how hard is this stuff to drill? If this stuff is super hard I have a wood lathe and can make some dowels to put in the through holes before I pour it to make drilling it later easier. This transom is a small one and already has roughly a 3/8" build-up of glass on it to the hull for strength as it only had 1 1/4" of wood inside(a piece of 3/4" and 1/2" screwed together and glassed inbetween, makes the chainsaw job interesting when you hit the screws) and then a thin layer of glass on the back. I've got most of it out already, and only have about 45 minutes into it so far. Hoping for some guidance from those that have tackled this job before. I plan on using ARJAY as I see they have moved and are only an hour away from me now.