Small block chevy, they recommend some crazy 500-600hp crate motors that are like $12k.
Seriously, check out the pricelist, it is very detailed:
http://www.ultimasports.co.uk/usa/prices.html
STAGE 1
LHD MIG welded round and square tube spaceframe chassis,
Fully bracketed to accept Chevrolet V8 engine with
Porsche transaxle, steering, fuel tanks, seat belts, pedals, radiator,
handbrake, gear linkage and brake servo mountings.
All powder coated in black satin finish.
$5162.00