We’ve seen fuse blocks put just about everywhere, from inside a voltage regulator housing to glove box, you name it. If space is an issue, could you not mount two fuse blocks? One for engine compartment and one for interior? To be honest, anyone who knows about old cars will spot your upgrades anyway. If nothing else, your battery size will give it away, or the brake booster and an alternator instead of a generator. Are you going with cloth covered wire instead of a cross link poly type wire? And so on...
Look at the “DelCity” website. They have some interesting fuse blocks and other items which may help you reach your goal. Good luck.
