Major update. I completely, thoroughly gutted the whole amp. Unscrewed and carefully unsoldered all transformers, drilled out the rivets for all the PC boards (damaged the phono board), unscrewed the faceplate, and threw out all the pots. I was feeling a bit OCD and besides, I bet I can wire it up more nicely than it came, with shielded wire etc.
My impulse at this stage is to bolt some perforated aluminum metal over the holes and point-to-point a new circuit, but there's really not much room under the hood for coupling caps etc. If I plunk in some ST-35 boards, which have a better reputation, the front panel becomes a bit weird if I don't actually include any tone controls. One option would be an active tone control circuit before the power stage:
http://www.angelfire.com/electronic/fun ... one-A.html
(the one labeled "Figure 14") At the cost of two 12AX7's, it seems like a pretty good one.
Tacking on a phono stage would be cool but I'm not sure the PT has the heater power to feed four 12AX7's..
Keeping the old chassis at this stage means drilling out more rivets, installing new RCA jacks and binding posts (disregarding the silkscreening), filing out an IEC socket, and installing new hum pots. Seems like a lot of work. I could replace the front panel with a piece of aluminum I get fabricated, maybe with some lettering engraved into it, but you can hardly call it a Dynaco any more...
Maybe I'll go to hi-fi hell, but I'm tempted to cut and run, and scratch build my own amp using the iron and tubes. I'll avoid all of the issues that come with salvaging what I can from the SCA-35. I'd use the PA774 with a pi filter, 3.3uF/5H 65R/470uF to put out ~340V B+, at 38mA/tube. I'd probably use an LTP with either a CCS derived from a tiny bolt-in transformer, or another negative voltage supply like in my most recent amp.
So yeah, I have a few options. Luckily I have some time to mull things over, and fix up my monoblocks. I might put them up for sale later.