New heat pump system with old ducting sanity check

I've had a few contractors out to quote me on replacing a gas-fired furnace (no A/C) with a new heat pump system and I'm getting different reactions about the existing ducting situation. Right now there's a 10x20 return air drop with a "T" connecting to 8x16 running both directions. Utility room is centrally located so approx half the house in each direction. Contractor A says existing ducting - including the existing return air drop - will support 1200 cfm adequate for a 38,000 BTU 3 ton air handler. Contractor B says he can't do more than 2 ton and that's with a new return air drop and radiused "T" at the plenum to existing 8x16 duct again running both directions 50/50. Which is more correct?

source https://hvac-talk.com/vbb/showthread.php?2226682-New-heat-pump-system-with-old-ducting-sanity-check&goto=newpost