You're correct Kenny, the 465 output shaft is not splined the full length, but only about 2.5 inches. It is 8" long outside of the transmission case.
The LONG 32 spline 205 input gear is not splined the full depth, but only the outermost 2.25 inches.
The SHORT 32 spline 205 input is splined the full depth.
If I remember correctly, the 465/205 figure eight adapter is 8" long, and the 465/205 round adapter is 10"long.
The 465 can be adapted to the round 205 using the common 465/208/241 adapter(8.5" long), but must use the SHORT 32 spline 205 input, and must use cable type shifter, as the adapter has no provision for a shifter.
Hope all this helps.
Jimbo
edit: You are absolutely correct about using the factory later model setup being easiest; it is also the strongest.
When GM went to the short adapter, the regular occurence of broken adpter feet disappeared, as did the premature failure of 10 spline couplers.