There's no real definitive info on Silverfaces, just a lot of hearsay. I've been all over the I-net looking this stuff up. Some guys with 67's will swear that for the there is no change whatsoever from Blackface on many of the transition models, and that's possibly true, although its certainly not written in stone and other will say '68 is the last year to consider, and that after that there's no real telling if the iron is manufactured to Blackface tolerances, and there's possible changes in caps form the blue ovals and changes to the cabinet and tone sucking bypass caps and phase inverter values and plastic wire and wax covered boards and all kinds of crap.
Too many guys I've heard, and I've heard plenty will swear NO Silverface sounds as good as a Blackface.
That having been said, I can understand someone not having a Blackface cause they can't find one or cannot afford one. Then get a Silverface and knock yourself out.
I don't "eff" with Silverface amps, because mainly I don't need to. IMHO, I'm with the camp you cannot get the tone out of a Silverface that you can with a Blackface, modifications not withstanding, although I would admit I've heard different as I said. I've heard many many people with lots of experience substantiate this opinion I hold, and to claim its any less valid than people who enjoy Silverface tone (which I adamantly do not) is absurd.
Please don't give me a list of schmucks who have played Silverface amps, that's entirely irrelevant as to whether Blackface sounds better than Silverface.