These work great, I've used them and if I'm not mistaken, so has Isaac;
http://store.triodestore.com/sdslabcapboa.htmlBut it will change (enhance
) the amps performance, most notably in tighter bass response and a slight output increase. It also gives the flexibility of using a SS or tube rectifier.
If you want to go the stock route, with those can caps that Oli posted about, KTL13
should plug right in (I haven't done it myself though, so caveat emptor), provide factory performance characteristics,
and also boost the voltage to a safer 550V from the stock 525V, which is probably a little anemic for the amp.*
*The 525V rated can cap has been a subject of debate going back to the original Dynaco Mk III's.