I've been running a 650 dp on my '64 and noticed a crack in the baseplate where the secondary shaft comes through. I could live with it, have the baseplate sleeved (possibly), replace it, or replace the whole carb. I chose the last option. The 650 seemed like a pretty well matched size, however...

I came across a heavily reworked, almost new 600 dp that is zinc plated (looks do count as this will go on a polished manifold), that would appear to easily outflow a stock 650 dp. I also figured that slightly smaller bore could give better non-peak throttle response at low flow, while the smooth entries could improve high flow characteristics. Was I wrong?

'64 coupe, 331 CI, Crane 222 degree (327/350 hp) cam, Edlebrock Performer RPM with 1" spacer, lifter valley thermal shield, Holley 650 dp (currently), K&N 4"x14" air cleaner, 427 hood with center cut out (cold air induction) 10:1 CR, Comp Cams 1.52 roller tip rockers, pocket ported and port matched 2.02/1.60 iron heads, Doug Thorley cermacoated headers, 2.5" mandrel bent exhaust with DynoMax MaxFlow mufflers, and 2.5" tips, Mallory HiFire IV and Mallory High voltage coil, solid copper spark plug wires, 4-speed CR, 3:70 gears, 225/60/15 tires.
http://abacus.sj.ipixmedia.com/abc/M...45d5/i-3_B.JPG [IMG][/IMG]

 

Looks do count that's why I have a Demon carb. If it's been heavily worked on were the throttle bores enlarged? I wouldn't think a 650 - 600 would be much of a change. Your one inch spacer if it's the open version would have had more effect on how it runs.