I've done to different installs on gauges. Both left the turbo on the truck and used the grease and magnet method. I have 50K miles on mine and it spools great. The other guy has about 10k on his and his is doing great.

 

Someone told me to stuff a shop rag in the manifold up to the point where u drill and tap. Pull it out when ur done and shop vac the hell out of it for good measure. Worked fine.

 

2 foot extension from under side for back bolts no problem.

 

Yes I was serious, doing it while running is pretty common. Infidel's method is probably a little safer yet. Truly the best way is to drill and tap it with the manifold off the vehicle but that is a little bit of work. I don't think I'd trust just the grease alone to catch all the chunks.