Well, I think that we are assuming that in the propossed scenario the war will be long enough to require similar number of weapons that in OTL. But I think that a Republic backed by other western powers since the begining could achieve a relatively quick victory, so maybe the production limitations of certain potential suppliers won't be a problem.
In first place, if the republican manage to block the moroccan ports during the first days, the bulk and the better of the rebel army is stuck in northern Africa. That probably would mean a hard time for the nationalists in Andalusia.
If anyway the nationalist can cross the strait, we will see probably a race between the two sides to build up their armies as it was not seen in OTL, and that also probably means a different strategy by the nationalists. They probably can't go with the "hold, exterminate, advance a bit, and repeat the process." without risking a serious republican counteroffensive. That could mean also a more troubled rearguard. i mean, if in OTL the republic could have won in the Battle of the Ebro with better air support, I think in this TTL we could see a major republican offensive early and with better means. Furthermore in this context, Miss Islas Canarias 1936 (as other nationalist generals called Franco because of his lack of definition to join the coup until the last moment, being a sort of attention whore) could be more doubtful, in a situation requiring more determination than in OTL although that could be meaningless and even we could butterfly Franco as head of the rebels. And las but not least, the lesser soviet influence could butterfly the (often) violent division between communist and anyone else in the republican side. In fact I'm wondering what is happening here with the militia "movement" and wether a western support would mean an early centralized republican army similar to OTL Ejército Popular.
OTOH, in OTL, one of the advantages of nationalists was the control the fertile agricultural areas in north-east Castile. On the republican side the advantage was in the control of the industrial centers and the bigger manpower (although less preapred for military tasks) In our case, the republic can get food and industrial supplies from other countries (a war is not only weapons) and it could help a lot.
Cheers.