They went to 32 spline and no coupler shaft in '81, but only the 208 equipped trucks. 205 equipped trucks (K30) retained the 10 spline coupler through '84.
To run a 27 spline 205 behind a 32 spline 465, you would need a new input shaft, input bearing, machine the case for the larger bearing and get an adapter to convert the case to round pattern. It would be expensive. Or you could get a later model round pattern 205, but those are expensive too.
By far, the cheapest and easiest solution is to run what you have. The 208 isn't that bad, just don't bash it on rocks, be sure to run a proper length front driveshaft, and run the stabilizer rod up to the bellhousing. Most people will never break a 208 with light to moderate wheeling.