in short yes and no mate ,
if your planning to fit the cosworth front end i.e cossie inner wings and bulkhead then the rst wings will need a fillet putting in as the arc of the rst wing is steeper then the cossie one ,
if your going rwd and want to keep the rst front end , just weld in cradel mounts and a tunnel ,
check my resto on here, will give you an idea whats involved in the front end ,
beef