The timing chain cover on my 351W is not setup for a front sump dipstick. The boss was cast into the cover but no hole. I have a 289 cover that has the hole but the water pump configuration is not correct for my application so I used it to fab up a fixture to drill out the hole on the 351W cover. I had a 3/8 transfer punch that lined up my guide tube with the inside of the cover.
I originally planned on using a single guide plate but there was just enough flex that the fixture was moving when I tried to drill it out, so I had to add a bottom plate.
I drilled from the inside and this was the hole that I ended up with on the outside.
