Wouldn't say a 16 is a big improvement, but it is an improvement. A 14 would be better but they are harder to find. 91. 5-92 will have a 21 housing, 93 should have an 18. 5 housing. IIRC the non IC trucks had a 19 housing but a small compressor.
An 18. 5 is only slightly better than a 21 and not changing the compressor wheel doesn't gain much at lower pressures where it is needed. An HE351VE is a big upgrade but a lot more work.