I personally like the under floor booster/MC kit. I have done several of them. The firewall set up is just more to clutter up the engine compartment and the pedal will not match the clutch pedal. If you are not interested in the stock look or have an auto trans it probably doesn't make much difference.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine