You should be able to do as much as you like in which ever aircraft are available (subject to the CAA minimums). Bristol I know for sure will let you split it any which way you choose - if youre flush and want to do the whole thing in a seneca then go for it but the majority of initial IR training
is best done in a sim. If a school cannot meet your requirements then look elsewhere! Thumbs up to Bristol they got me through both first time