Tom,
You asked about timing. I would recheck that, as well. My COE ran smooth, but seemed to be losing power, maybe not as severe as you describe. Turned out the clamp on the distributor had loosened and the timing became too advanced.
Kent

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix