Glad it came apart. Once you know how it works, its a easy job. I used new stock replacement springs on the front of mine with three leafs removed from the bottom of the stack. The rears are still original. I used the 1 3/4" spring pads froma '55 Chevy rear axle. You can get the spring pads from any trailer shop. Other then the spring pads, the axle is stock 3.08 '79 Firebird 10 bolt.
The front axle is a stock '55 Chevy truck, it was in it when I bought it. The only difference is the king pin diameter. The disk brake kit is from (
www.mpbrakes.com/ ) Master Power Brakes.
Its a bolt on kit using stock GM parts. Mine are manual brakes but you can add a power booster if needed. I like the way mine stops, but some think its a little stiff.
As far trans and engine go, the 250 is a good choice but requires new mounts and cross members. I would go with a 200R4 or T350 for a transmission, stay away from the power glide. A over drive and a 3.42 rear gear or 3.55 would be just right. My 3.08 with out over drive works good on the highway but is just a touch to high for around town and stop light to stop light. It was a lot peppier with the 3.42 but ran to high rpms at 70+ mph.
Joe
