Geez, I forgot about this thread...
Regarding the "converted" freighters, if we're going to pull the Mon Calamari analogy, then you should follow it through to its logical conclusion. The Mon Cals "modified" their own starships for combat. And even then, it would be absurd to assume they continued building warships for years after contributing their fleet to the Rebels as "peaceful" ships and then went back and converted them. They'd build them from the ground up as warships after their initial vessels were converted. (And in the four or so years post-Yavin there would be plenty of time to build new warships.)
In any case we have no evidence that they were somehow provided or crewwed by anyone other than the Alderaanians - the context of the quote is that warships from every member of the Alliance (includinb the Mon Cals, Corellians, Bestinians, Kesselians, Sullustans, AND Alderaanians) were assembled (along with other vessels not specifically identified as belonging to those parrticular groups.) without further evidence ifor the "possibilities" being suggested I fail to see why they should even be considered simply because "ALDERAAN MUST BE PEACEFUL!!"
As for the whole "Alderaan providing money for munitions rather than munitions itself - why the hell would they say "munitions" if they meant money? Money is a much more liquid asset than weapons are - the Rebels could use them to purchase much more than just weaponry (ships, medical supplies, food and drink, vehicles, etc.) And most of those would probably be more plausibly denied than munitions would. (IIRC from the Radio Drama Princess Leia used the pretext of humanitarian aid to beleagured systems to spy for the Rebels.)
Oh, and as a last bit I forgot about this tidibt. I don't remember where the "fleet numberS" bit came up, but its worth noting:
Rebel Alliance sourcebook, page 91 wrote:
"As you can see, by the numbers, the picture is pretty bleak. The Empire's forces outnumber the Alliance forces by a factor of almost 30 to one in raw manpower, by better than 12 to one in equipment, and by about 15 to one in warships and transports. The numbers are equally grim when you compare weapons research, intelligencee, and supplies"
How those numbers actually break down is not specified, however, and there is some room for interpretation. It is worth noting, however, that such numbers would be a requirement for the Post-Endor activities of the Rebels - they would need a substnatial fleet available (nevermind other forcese) if they were to successfully prosecute an offensive war to take territory from even a disorganized Empire.