wheel back spacing

[jh68c10]

I'm about to order a set of the boss 338 wheels for my 68. I have converted the front with a complete 74 front suspension. And put 5 lug axles in the original rearend. I know the rearend is narrower than later models. What back spacing do I use to make the front and rear look the same width. I don't want the rear narrower than front. Thanks

[ecgate]

I would like some info on this also.