The wheel and tyre combo looks fantastic.
205/60/15 is very close to the OE rolling diameter for the 175 / 78 series tyres. You can play with the numbers here.
http://www.rimsntires.com/specspro.jsp
AFAIK, the rear springs changed from a double pigtail to a single pigtail and seat from the 1973 year models onward, however it's easy enough to interchange.
While 240 rear springs will probably work fine in a 140 /164, it may be worth mentioning that one can't use 240 front springs in a 140 / 164... uhhh, well, you can, but it will seriously mess it up.
Remember that the 140 / 164 is a double wishbone suspension, not a McPherson strut. So the wheel rates are different to the spring rates, because you have to put the motion ratio of the wishbones into your calculations. At the 164's roughly 2:1 motion ratio, the standard 380 lb / inch spring in the 164 works out at about 170 pounds wheel rate.
Bit different to a strut where wheel rate = spring rate.
This is why you see some crazy big poundage numbers on wishbone suspensions for the street.
164 front springs in a 240 would loosen some peoples' fillings.
240 front springs in a 164 would also be virtually undrivable (75 lb / in wheel rate).
