When I put a new reverse gear in the Fiat I only sheared 1 bolt from the bell housing and had the magnet from inside left when I had done.
When I was changing the glow plugs on the Ford I only sheared 2 off, 2 work though.
When I drained the water off the MDIIC I only broke one of the three drain taps, I stoped when I broke the first one.
It may be best to pay someone to do it.
I used to shear off every bolt I tightened etc etc but I persevered. A lot of the guys who will charge you £30 per hour or more to work on your engine will do no better and will also charge you for the time they spend fixing their own mistakes. Have a little faith, or get another forumite to come and give you a hand.
When I fitted the new Beta to Fairwinds I bottled out of aligning the engine. The end result was I paid a 'professional' nearly £400 to misalign it TWICE!
. He had the propshaft nearly touching the side of the stern tube; it was so badly misaligned that the Volvo stern seal leaked. 'Oh, must be a fault in the stern seal', he said - until I pulled it off and showed him what he had done. (Don't do this on a boat with a normal cutless bearing in case you sink btw).
It was fine when I did it myself, absolutely fine and has been for 600+ hours.
Really, seriously, do it yourself - seek help here with every step, invite mates to help and feed and water and flatter them, but stay away from boat mechanics if you value your liquidity and sanity. Many are useless, none that I have heard of yet offer value for money.