(Wish I could figure out how to indent an excerpt and interleave the response. Doesn't appear possible on this board.)
BC-611's are a pain to work on compared to most larger sets (voice of long experience speaking). Some parts (tubes for example) are still pretty readily available. Others much less so. Typical going price for one radio in good condition is $150-$200. And that's my definition of good condition, not that of some yahoo who doesn't know a BC-611 from an MB.
In order to tune a BC-611 successfully, the chassis must be inside of a test case. If you tune it outside of the case (except for the receiver IF's), putting it into its case totally detunes it.
There were two test sets built for working on the BC-611, the IE-17-(*) and the IE-37. The IE-17-E is the preferred set, and consists of I-135-E, F or G Test Set, CS-81-(*) Test Case, FT-252 Test Stand and A-82-(*) Phantom Antenna. Plus a transit case and some minor components. The I-135 has a cable with a connector that plugs into the bottom of the radio chassis. And a multimeter that can be switched to measure the various voltages or functions, a microphone and earphone, an audio oscillator to modulate the transmitter, and a crystal test oscillator. The CS-81 has cutouts or holes over the coils or capacitors that must be adjusted. The FT-252 holds the CS-81. The A-82 you can get by without, as it is only used for a final check of modulation versus transmitter loading.
The IE-37 might be called the poor man's tuning set. It consists of a CH-312 test case (with cutouts for tuning) and a bottom cover similar to the one on the late BC-611-F, with a phone jack and a couple of pin jacks. With it, you use the internal batteries to power the radio under test, and another radio with a second special bottom cover (also part of IE-37) as both a detector for tuning the transmitter you are working on and a signal source for tuning the receiver. With the I-135, you use external batteries or power supply (I use a power supply).
You can make an ersatz test case out of a radio case and a late -F bottom cover (all original CS-81's were made from BC-611 case castings). But I wouldn't do it unless the case were damaged such as not to be usable on a radio. Instructions for drilling and slotting are in the 1945 TM 11-235. And use a standard signal generator for tuning the receiver and a field strength meter for tuning the transmitter.
FWIW, I-135-B is for the BC-721, but I have only ever seen two of them. I have never seen an I-135-A, C or D.
On the crystals, 3885 KC ones are becoming quite scarce. But if you ever come across a dud, don't throw it away as aside from corrosion or physical damage, they are 99-44/100% repairable. I have come across a lot of dead FT-243's. But I have never seen a bad crystal unless it had been physically cracked after being removed from the holder. There are in each FT-243 two brass contact plates with thin legs that go down into the pins where they are soldered to the pins. Every dud I've ever opened up had one or both legs broken off right where it leaves the plate. I've repaired many by salvaging plates with intact legs out of crystals made for sets no one is ever interested in. But the donor and the recipient pretty much have to have been made by the same contractor as they mostly all used different shape plates. Sorta like having to have the same blood type.