I agree with your second post about the added security of a pin. You could also grind a flat spot into each of the shafts before adding the sleeve, then press the sleeve into the flat spot before you weld it. That way you would have a positive lock like a spline for added strength.
Just another idea,
Scott

Scott Ward

2 1948 1.5-ton Loadmasters
The red one and The snow pusher
1 1950 3100
1 1955.1 Chevy 6500
1 1954 Chevy 6500 2-Ton
1 1955 1st Series COE 5700
1 1963 K20 (454)
1 1964 C10 (350)
1 1951 1.5-ton Dump Truck
1953 and a 1956 Ford F800

Raising a teenager is like trying to nail Jello to a tree!