Kamuics

ok so i have a 99 si with k20 swap and the subframe has been switched to an integra one and on the driver side the nut that attaches the lower control arm bolt to the subframe has broken loose on the inside, pretty sure its supost be welded in there, and i cant get the bolt to go in. i need to know what are my options to fix it. i can only think to drill out the hole just below it to reach in just worried about structurally weakening the subframe. or should i just buy new one?