Common Considerations from my notes:

1. Horsepower Rating or Displacement 
2. Engine Orientation 
3. 1. Horizontal 
   2. Vertical
4. Dimensional fit up 
5. 1. Mounting footprint 
   2. Length
   3. Width
   4. Height
   5. Crankshaft centerline
6. Crankshaft:
7. 1. Diameter
   2. Length
8. Air Filter Design 
9. 1. Design 
   2. 1. Flat
      2. HDAC
      3. WAWB
      4. Customer Supplied
   3. Mounting
   4. 1. Engine
      2. Remote
10. Closure plate 
11. 1. Bolt circle
    2. 1. Common Variations 
       2. 1. 5.00"
          2. 6.50"
          3. 7.75"
    3. Pilot 
    4. 1. Common Pilot Rings 
       2. 1. 5.75"
          2. 6.438" (6-7/16")
          3. 7.0"
12. Oil System 
13. 1. Remote filter 
    2. Oil Cooler
14. Dipstick
15. 1. Fill Tube 
    2. Bayonet
    3. Dipstick
16. Ignition Group 
17. 1. Charging amperage
    2. Key switch 
    3. 1. Included 
       2. Installed 
       3. 1. Mounted
          2.  loose
    4. Wiring Harness
    5. 1. Requires RP1 kit?
       2. EFI Jumper 
       3. 1. Required
          2. Part Number 
    6. Other Considerations 
    7. 1. Anti-icing heater
       2. E-Gov
       3. ETB
       4. Dual Fuel
18. Other Options and Considerations
19. 1. Short Block/ Long Block availability 
    2. Front shaft
    3. Controls 
    4. Fan screen
    5. 1. Grass Chopper 
       2. Front shaft hole
    6. Muffler and shielding
    7. EPA regulations  
20. Availability
21. 1. Current production
    2. Old stock.