Hi Colin

You are right to be wary, As you say very thin long bolt

The water ways in the head are also close to the bolt and as the drill constantly wants to be in the softer aluminum its not a simple job to do....

there are guides on the market to drill these out (which we have)but it is still reliant upon a small flexible drill cutting in a perfectly straight line.

We avoid doing these for those reasons, and we are busy enough anyway.

try the snap on type easy out with the fluted bar you tap into the hole, the bolt sometimes loosens off when it breaks and the load is removed

Can't recommend anyone in your area but can advise against a few !!

pm me

tony