Vintage Synth Repair

As I'm working recently on recapping of all my machines older than 20  
years, I'd like to ask more experienced colleagues here few questions:

- In Old Crow's document about repairs of vintage synthesizers it's  
recommended to change all tantalum capacitors for standard  
electrolytic capacitors of the same value. Why should it be done? I  
suppose there had to be some reason why there was used tantalum in the  
original spec...

- Should I add capacitor to each IC's between plus and minus power  
lines where they are missing? If yes, which type and value should be  
used?

- Where I can get big high power can multiple capacitors for old  
Hammond organ tube pre-amp and amplifier in Hammond box HR40? I know  
suppliers for Hammond and Leslie components but they seem to have not  
combinations of value I need.

Thanks for advice.

Daniel Forro