Thanks for the heads-up sam!

I went back out to the garage and did some looking and my fingers (with dental tool) saw something I didn't make out at first with my eyes due to the light (hard to get light down a 3 inch hole where I can still see) anyway, what I felt, then saw was about a 1mm radius difference between the blind hole in the block and the channel though the head. It looks to me as if I can do this in-situ perhaps scarring the channel with the new tap, but nothing which would cause permanent harm. I'll get the kit and if it doesn't fit through the channel, then I'll pull the head and order a new set of bolts & gasket. (I'd just like to avoid the hasstle!)

Thanks for the advice, I appreciate it alot!

Scott