Hello Does anyone know the realistic BHP limit of this manifold?

I know it's not a particulary nice lump of cast iron and has its limitations but I've got a million and one things to buy for my Mk1 Escort so I don't need to be spending ££££ on "gucci" manifolds just yet!

Basically I'm in the process of putting together a brand new 2.0 Black Top Zetec-Turbo engine for my 1975 Mk1 Escy (Thought I'd move away from the YB trend on cost grounds!). It has/will have...
steel rods,
ARP fasteners throughout,
Forged low-comp pistons,
standard cams,
Nissan 200sx SR20det RWD inlet manifold (machined to fit zetec head)
RadTec "YB" intercooler and radiator setup
440 cc injectors
Haltech E6X engine management,
Coil-on-plug leads
3-bar map sensor
Boost control solenoid
Wide-band lambda
Garrett GT25 turbo (may go for GT28 or "disco potato" yet! )
Bespoke exhaust system using 200sx elbow and downpipe
Going to run 14 PSI

I'm after 270-300Bhp Guys, do you think I'm being realistic with this setup?? I'd be happy with anything over 250bhp TBH though as it's the TORQUE I'm looking forward to after owning loads of peaky N/A engines that idle like crap!!

Thanks for any constructive replies everyone!