I just got a '78 today. It has awesome tone. No need to screw around with blackfacing it, removing the pull boost, or even upgrading the stock speaker. This thing fricken rips and has tone for days. The minute circuit changes CBS did to the late 70's SFDR's have minimal effect on the tone, and I'd even venture to say at this point, I think they made it better due to the larger tranny they put in it to squeeze a touch more headroom out of it. Mine is breaking up gorgeously around 5-6, but with a softer pick attack it is clean and shimmery. This baby is a total keeper. As a reference, my main gigging amp is a '71 Pro Reverb and I had a DRRI kicking around for several years that I recently traded away..but this '78 SFDR is miles ahead of the DRRI in tone. Miles.
These amps get no respect due to the pull boost (which is a stupid feature), but I'm telling ya, they are keepers. Get one now. I'd say a fair price to pay for a good condition one w/ cover and footswitch would be around $800. I did a bunch of price research on them and while you can really shop it and get one for $150 less, the $800 is about average for a pull boost version that isn't hammered and/or has issues. Don't be afraid of the late 70's era for the Deluxe Reverbs..CBS didn't mess with the smaller combos like they did the bigger combos (twin, pro reverb, etc) with the master volumes and linear trannys and all that.