'73 Power brake upgrade-booster?

[MARKDTN]

There are a whole lot more 75-87 trucks out there than 73-74-most with power brakes. I was hoping to find somebody to say, "yes, any square body booster will work on a 73-74 if you do XYZ". Or maybe "yes, 73-82 all bolt up to the firewall but the master cylinder is different". Or something like that. Maybe I have to have a power brake pedal? I know that I can buy a 73-74 booster from Ebay or Rock Auto, but I think I can find used for much less. I'm not worried about the fittings on the master cylinder; I have a Mastercool tool and can make new lines if necessary. I'm just trying to find out what vacuum booster will physically bolt on to a '73 without cutting new holes in the firewall or pedal support bracket. Then I can hit up friends and junkyards and find one. I will buy a new master cylinder, but I can't do that until I get a booster just in case they have a different bolt pattern. Thanks!