Smaller brake booster....if need be. Is it a problem going in with the motor or after it's on the mounts because it might be ok after you get it on the mounts.you might have to set the motor in with out the brackets on the motor to get it in the tunnel and on the transmission mount then put the brackets on.

 

 

Do you have stock valve covers.

 

Resources: Big Block Truck Kit

Power Brake Booster Notes For Big Block Truck Conversions

If your truck is a D, AD, W or AW 100/150 that came with factory Power Brakes, you must identify the style booster on your truck, two styles were available, the Single Diaphragm booster was large in diameter and sat flat against firewall, it measures roughly, 11 1/2". The other version, called a midland or dual diaphragm booster measured, roughly 8 1/2". If you are installing a B Engine, 360-383-400, either booster generally will not cause any value cover interference when using production style valve covers. If you are installing a RB Engine, 413-426-440, you must use a Midland Dual Diaphragm Booster with original Equipment Style Valve Covers.

Aftermarket or aluminum finned valve covers will not work unless you use the Midland Dual Diaphragm Booster and relocate booster mounting point, at fire wall, sometimes as much as 1" further away from engine. These are easy to install, just unbolt your master cylinder, (no need to loosen lines from master cylinder.) pull out away from booster. Then just go inside and remove mounting nuts from studs and push rod from brake lever. Reverse Removal procedure for installation.

Since 3/4 and 1 ton Trucks come with heavier duty brakes, they already have a smaller booster. 1972-1978 Brake Boosters are only available in 2 bolt master cylinder styles, no 4 bolt style boosters available any more.