i'm reading Richard English's book atm, which seems to concur with what else I've read.I've got a bit more to go through, Mcallister's paper, plus a half dozen others, and a fair few books. as well as some documentds that sinn fein themselves put out during that period. Considering what I've got here, i doubt another study would make a lot of a difference.
and if you're measuring support through election success, then of course, that can only be done from the 80's onwards, when the decision was made to begin to contest elections. they clearly were able to engage with the community during the beginning of the 80's, although that level of support was dropping towards the end of the decade, IIRC i've got a peak by 1984.
what i'm talking about is a lack of mass support for armed republicanism prior to the prisioner protests. their support was certainly higher than in the 60's when the number of active IRA supporters was almost negligable in the north, but I'd seriously doubt their ability to have won elections on the scale they did in the early 80's before the hunger strikes, even had they ended their policies of political abstensionism at that time. they just did not have the level of support needed for that.