Worth the effort?

Besides tuning, did he do any diagnostics on the engine? Specifically cylinder pressures or leak downs? I've found some issues with cam degreeing, valvetrain geometry, timing, and ring issues on "great running" engines by doing those when other things were suspect. If the convertor is a good one (I'm not familiar with SMR but have heard the initials before) then I'd still be looking elsewhere before I threw money at the trans. A 340 in an A body should be able to spin the tires 1/2 way thru first totally stock with mild gears. If the response is slow, I'd be looking at cylinder pressures.