Howdy TC:
If you have the schematic in electronic format, send it to me - look for my email address in PM. Warning: if you spam me, I'll make a voodoo 'tube' out of a 6L6 - short circuit it or something - your amp will never work correctly...kidding of course....sort of....
I have dozens of carbon comp and metal film resistors; 1/2 and 1 watt and 5 and 10 power resistors; free to a good home. Also have one remaining 3X40uf/450V Weber multi-section cap w/ mounting hardware...ought to do it for your unconnected can-cap; how many multi-sections are in there?
Nothing wrong w/ tube rectifiers; rugged, reliable, and in good supply although they are more prone to 'sag' which, depending on your point of view can be good or bad; alters tone some but one man's treasure is another man's trash. During the mid-60s, alot of manufacturers transitioned to solid state / diode rectifiers; chances are Howard's schem is a later version of the same amp.
Tube amps with diode rectifiers need a 'stand-by' switch or position on the power switch. When turned on, a solid state rectifier puts B+ instantly on the tube plates however the filaments (heaters) need time to warm up. If they don't get the time, electrons are 'stripped' off the cathode stressing it and shortening the tube's useful life. Because a tube rectifier also requires time before it will conduct, amps using tube rectifiers don't have this problem.
Years ago I was fortunate to own a Marantz 10B tuner; Saul Marantz's 'last (tube) word' on the subject of tuners; 21 tubes including rectifier. Before you part out the organ amp, you might want to consider making sure you either have a schematic or can confidentally identify the value of components. As ever, the devil is in the details...2X6V6s...good for about 15 watts; I don't know the EL84 at all which has a similar power rating but 6V6s are pretty versatile; sharp and tangy to smooth and, depending on the speaker, break up nicely.
Leave your mis-matched 6L6s in the amp until the power supply is stabilized and you have a fresh cathode resistor with parallel cap; then you can get a matched pair; going to run $35-$50 - which is why the power supply and cathode cap need to be in place before you re-tube; if not, you'll have a brand-new mismatched pair instead of a used mismatched pair....
good luck...let me know if I can help.