[Amps] Question on by-pass capacitor TYPE

[N1BUG]

I have a question related to recent discussion of my amplifier 
oscillation problem and need for better by-passing.

I am not particularly knowledgeable about the relative merits of 
various capacitor types. For reasons long forgotten I have always 
used disc ceramic caps for by-passing in amplifiers. In digging 
through my junk box (aka house, same thing) I found some 0.1 uF, 
1000V polyester film caps (C-D part # DME10P1K-F)

Data sheet:

http://www.cde.com/catalogs/DME.pdf

Is there any reason I shouldn't use these for by-passing at the cold 
end of the the cathode choke and possibly grid resistor? To 
reiterate, this is a 4CX1500B amp with the screen connected directly 
to chassis, -330V or so on the cathode. It is cathode driven. 
Although this is not the amp in question the configuration is very 
similar to:

http://www.n1bug.com/tech/4CX1500B-6m/6m4CX1500Bsch-hires.jpg

I am asking about using these caps in parallel with the existing 
1000 pF feed-through caps at C6, C7, C8 in that diagram.

It was suggested I add a 1 to 10 uF cap in parallel at C6. I see 
they make these polyester film caps up to 1.8 uF in 630V rating. 
Would that be better or worse than using an electrolytic? The 
voltage rating would be a little more comfortable than electrolytics 
as there is about 480V across C6 and C7 with the amp in standby.

Thanks for any input.

BTW: I also found some C-D 160104J1000N-F metalized polyester caps 
(0.1 uF 1000V) but the case and lead style does not as readily lend 
itself to installation as the former type.

http://www.mouser.com/ds/2/88/160-10085.pdf

73,
Paul N1BUG