garyg,
My unprofessional opinion. The hydraulic engine would be inherently more quiet from a lifter standpoint, no question about that. The solid lifter engine should make some noise, but shouldn't drive you out of the cab, even when cold.
As a youth, I always thought a solid lifter rig was snappier than one with hydraulics. On one of these old engines, you probably couldn't tell the difference.
I think a properly tuned and adjusted solid lifter motor will purrrrr just as sweet as one with hydraulics, BUT, you will hear (and should hear) some slight tappet noise. Many folks feel this light tappet noise gives these old engines character.
If you spend some time adjusting your valves perfectly, you might be surprised how much they quiet down. I wouldn't switch engines just for hydraulic lifters, but this is a personal choice.
Stuart
