think a GRPA coil wuld be wasted money imo, theirs no need for it really, what plugs do u use? are they gapped correctly? im not sure what plugs u need for different specs but mine r NGK BC8 RES and have no probs, jus std tho
anyway, i dont think the loud "pop/bang" would of done any damage to a plug as the explosion of unburnt fuel wuld of happend in the exhaust. if its miss firing now then check dizzy cap/rotor arm/plugs/leads, also could it be missfiring as a result of you changing the ignition timming?

get it to a well known rr who know their stuff and explain all your symptoms/problems/thoughts, tbh their ws prob no worries with it after it got set up, u maybe jus parranoid as u said b4

dont worry bout the poppin an bangin at all btw........