[Hallicrafters] S27 Receiver Problems

[Alf Fisher]

Hello everyone,
I have a S27 receiver that is VERY quiet and I am trying to fix it.  You guys must have accumulated a vast amount of knowledge about this model and similar ones.  I'm having some difficulty because the set has been modified in the past and there are a number of things that aren't as they should be and I want to restore it to proper working order.

On investigating the circuitry, I find that  the first audio / phase splitter tube isn't  a 6C8 but is a 6SL7 as used in the S36A receiver.

I notice that all the tube bases are riveted into the chassis. It may have originally had a 5Z3 rectifier and a UX4 base, but the base has been changed to an octal one fixed with self-tapping screws - presumably for a 5U4 but there isn't space to plug one in, because the guy has replaced the mains transformer with a drop-through type that's fixed into 2 of the old transformer fixing holes hence it covers over half the octal holder.  He has soldered a couple of 1N5407 diodes onto the octal base tags underneath and there are 2 wirewound resistors that get very hot.  It may be possible to make a subchassis to mount the transformer in its proper location and I can then put in a 5U4, remove the diodes and limiting resistors and drastically reduced the heat dissipation under the chassis.

The BFO control has been removed and there are some wires that have been cut off from somewhere.  Does anyone have a clear photo of the underside of the chassis in the region of the BFO?  The ones in the manuals on the interweb don't have the detailed resolution to see what is going on in there.

Please can someone tell me what size are screws that hold the S meter in place. 
This guy has used some M3 screws but they lock up within half a turn so are clearly the wrong thread.

Apart from the **modifications** done by its previous owner, are variations like these are common; this is the first S27 I have ever worked on.
I found a few resistors way out of tolerance - like 250k that measures 630k but I guess this is fairly normal for a set of this vintage.
Thank you for your time taken in reading my posting and hopefully you can help.

73,
Alf
G3WSD