I have seen it done many ways, how do you go about sealing up the coolant passages for you have done your peripheral port?

The way I like the best so far is using a little high temp RTV first and then filling with the liquid version of JB weld. I feel the RTV creates a seal then the liqued JB weld seeps itself into cracks a crevices better then you could by pressing the puddy in.

 

I'm in the process of building a 13b pp motor(being built by CLR Motorsprts, Carlos Lopez) I bought devcon liquid aluminum putty, and it's not cheap

 

I used Devcon as well.