Use of the impact driver will save you a bunch of heartache and hardware. When I originally took apart the engine, I stripped and ruined a bunch of screws that I eventually had to replace. The oily engine and excited first time builder are a recipe for a bunch of destroyed hardware. Using this tool will allow you to avoid a bunch of problems.
If you do destroy hardware, and you can’t get it at a Lowe’s or Home Depot, Mr. Metric has about any piece of metric hardware you could ever need in multiple finishes.
Impact Drivers are cheap. $8.99 at Harbor Freight.