Hilarious - Here are some snapshots of the stock tire and wheel data details from the
1946 Chevrolet Truck Data PDF at the GM Heritage site.
Are you planning to run stock 15" rims or another wheel? The RPO optioned 15" rims are listed as 5.50" wide and the tire details indicate that a stock 15" tire used a 7" tube, which is probably where the 7" wide tire measurement comes from. A little web searching indicate the recommended minimum rim width for the 215 tire is 5.50", so you should be okay with the original RPO wheels if that is what you have.
The difference in width between the 205 and 215 tire is only a little under 5%, so not much difference and may not be a significant change to your steering effort level.
The taller, skinnier tires (16x6) do make steering a bit easier, but the call is yours based on what you want for steering effort coupled with other factors (appearance, stance, etc.).
I'm interested in seeing the result of your choice.
EDIT - I missed your mention about getting some modular wheels. 6" width will suffice for the 215 tire for safety standards. From there it all about appearance choices I think.
