newbie with questions

[mark100]

Hi all
ive not got my book yet so can i ask a few opinions please
the car to be built will be a track , hillclimb car trailerd to events so no need for the mot and tax....
Can the chassis take over 300bhp or will it need extra struts ?
My options for doners are nissin skyline gtst (2.5 turbo straight 6)
or subaru imprezza (ej20 flat four ) So how much space do i have to work with in the bay ?
ive seen the odd nissan sr20 units used but not seen the rb25 unit does any one have one (or treid to and failed if so what was wrong )
will the hubbs be useable as id like the brakes and extras to help keep costs down
Thanks Mark