I've had a vehicle without power brakes. I would say go ahead and take the weight and complexity hit and do power brakes. As for power steering, if the front end weight of the vehicle is fairly light, non-power steering can be quite acceptable. If you go with rear or rear-mid engine, the front will probably be plenty light to go with non-powered rack and pinion steering.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.