First of all map, welcome aboard.

My first suggestion would be for you to drive the car around awhile (meaning more than once) and see if you can live with the manual steering and brakes. If you're not use to them, it can seem like a lot of effort at first, but if all you're doing with the car is occasional "pleasure" driving it may be satisfactory. Steering will be real "tough" only when the car is stopped or nearly so, and you're trying to do tight maneuvers. Rollin' down the road, and doing turns shouldn't present much of an issue unless you're one of those spaghetti arms. If the brakes are in good working order, you'll have to stand on them a fair bit harder than you're used to with power brakes. If they're not operating properly you'll be in for the time of your life. My last tri-5 was the '56 wagon and the manual steering posed no problems. Like 93 did, I put dropped spindles, short coils, and disc brakes on the front, and those kits always come with the power booster.

Part of what determines if you want to do the upgrade is your overall plan for the car. Now I'll preface my remarks by stating that I'm not a big fan of dumping a lot of money in a four door car. Everything you do costs at least as much money, and time, as you would spend for a two door car, but when (notice I didn't say if) you go to sell it you don't get as much of your money back because there's too small a market for the four doors, and people usually buy those because they're cheaper (that's the result of low demand too) and aren't as willing to pay the premiium for the upgrades. If you absolutely love the car because it is a duplicate of your first car, or your grand daddy's car, whatever, and you don't care about losing all the money you dump in it, then go for broke.

Finding near 50 year old original parts will be a challenge. The tri-5's are some of the most popular cars in the hobby so there's a lot of support out there for them, but also a lot of competition from the hard core restorers for the original parts. I'm a modification (rodder) type, so I haven't paid too much attention to the stock restoration stuff, but there might be reproductions of stock style power brakes and steering being made. But I'd be surprised. If you stayed with the original suspension, and drum brakes on the front, then all that's needed is a vacuum powered booster that mounts between the master cylinder and the firewall. You'd probably have to change a little plumbing and the push rod from the pedal arm to the master cylinder.

The steering is another matter. The originals mounted the power pump to the back of the generator and that actuated a ram mounted to the tie rod below the engine. They worked okay, but would be hard to find in good condition today. The other alternative is to switch to a 605 steering box, places like the one 93 mentioned often sell kits to do that. All up they'll run something over $1K. The 605 is a later model (relative to the 57) GM steering box that has the power assist within the steering box itself, so makes for a nice compact setup. Also, since it's newer engineering, it has better "feel" than the stock box (which isn't really all that bad). If your car still has the stock engine and motor mounts it could be a challenge finding a place to hang the pump. The original 265/283's, and probably the 235's didn't have the extra bosses cast in the block for front bracket mounting. Part of the bracket would mount to the water pump, but the other mounting points might not be there. That would be a good question to ask the vendor before plunking down your money. If they've put in a later engine you might have the mounting bosses. Again, check.