It's never a bad idea to go with the Canton pan, EVER. The extra volume gives you a tad more "heat sink" effect, allowing the oil to cool a bit longer in between passes through the motor, AND control of sloshing away from the pickup with the proper baffles is a big help.
The ideal time to put on on would be when you've already got that K-member out of the way to put the tubular stuff in like you were planning on already.
I'm at Detroit Speedworks full time now, feel free to call me up and pick my brain during the week... BTW, the chassis dyno is due within the next week or two...
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Greg Banish
President,
Detroit Speedworks, Inc.
'93 LX Turbocharged Road Racer
'00 Bad-Ass F150