If it's a Sentercel rectifier - a tubular Paxolin jobby - it will most likely have a series of discs in it.
I've attached a couple of pictures of one that I dismantled (in a Heathkit Res/Cap bridge) and replaced with a silicon diode and limiting resistor, (because silicon diodes produce a higher output voltage than do selenium rectifiers, a series resistor is needed to drop the voltage to that desired), but that was a half wave rectifier. Yours is a full wave so will have two connections for the AC input, and two for the +/- DC output. (I'm puzzled that you say it has eight connections).
The first picture is the Sentercel stick before dismantling, the second shows the disgorged contents and the replacement silicon diode and limiting resistor which I re-stuffed the Paxolin tube with.
Before condemning the rectifier, I'd be inclined to first check the AC Voltage input to it (no voltages are stated on the circuit), and compare that to the DC output. I'd expect the DC output to be a little higher than the AC input to it if the rectifier is healthy, but if it's appreciably less, it will need replacement. The easy option would be to fit a 'WO' silicon bridge like the one shown here, which would be more than adequate as it's 400V at 1.5 Amps:
https://www.ebay.co.uk/itm/2-WO4-1-5...4AAOSwDX9b5dGk
Or if you preferred a higher Voltage rating, you can get them up to 1000V.
EG ten for £2.00 here from a UK supplier:
https://www.ebay.co.uk/itm/10x-BRIDG...r=530257631312
If you'd rather steer clear of eBay, RS, CPC/Farnell, Rapid, Cricklewood, ESR - whoever.
The marking on these little round 1.5A bridge rectifiers denotes the Voltage rating: W02 = 200V and so on:
W02 1.5 Amp 200V
W04 1.5 Amp 400V
W06 1.5 Amp 600V
W10 1.5Amp 1000V
The alternative, if you wanted to try to preserve the originality, would be to use say four 1N4007 silicon diodes and a limiting resistor if they'd fit inside the original tube.
It's possible, if not probable, that the two 8uF smoothing caps will be past their best, so it's worth checking their capacitance. They may respond to reforming, or you may want to consider replacing them, though I'm not saying you should. Likewise, before just replacing the tubular capacitors on sight, if you are able to test them for leakage at their rated voltage (with a Megger or similar insulation tester for example), and also check their capacitance, that will show whether replacement is called for.
It would be sensible in any event to replace the two 0.002 filter caps on the AC mains input, which would need to be Class Y caps as they're from Neutral to ground and Line to ground.
Before you dive into it, you might want to see if it's operational. You could try it on a lamp limiter, look at the waveform of the unmodulated and modulated output on the scope if you have one, and check the frequency on a counter, or if not, check it against a radio on a range of stations.
As to the dummy aerial, the component values are shown on the circuit, so it wouldn't be difficult to house them in a small metal canister rather like those that Denco coils used to be supplied it. (I made one some years ago, housed in a small metal salt pot). I assumed that the 70 Ohm resistor on the circuit where the dummy aerial plugs into the attenuator socket is figurative - to indicate a 70 Ohm coax lead, rather than an actual 70 Ohm resistor.
Hope that helps a bit.
Every good wish with it Christian.