Removing the intake and exhaust manifold if not already necessary is asking for more work and possible troubles.
Even with the manifolds off and at the drill press it’s not an easy job to block, clamp, shim, adjust, and check before drilling. The manifolds aren’t flat on the bottom.

There are drill and tap guides available, or make your own temporary ones with a block of wood and a drill press.
https://www.shop.biggatortools.com/main.sc
With those to help drill and tap a somewhat less skilled person might get perfect results. In any case experience leads to skill, neither comes without trying new things.

Without those guides go slow and check drill and also tap for square at two points 90* apart with a small square, even a business card is a handy square.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-