wheels/tires and suspension together for project

[danman987123]

I am in the process of building my truck...got the frame all together....its pretty much a cab/chassis. has the drivetrain and cab sitting on the rolling frame...now i would like to start lookin at suspension and wheels. for sure im getting 20's and it will be lowered lookin about a 255 in the front and a 285 in the back. now should i buy wheels put them on my truck with tires then mount the fender and measure the gap between tire and fender to see how much i would like to lower it.....OR do i just order spindles, springs, wheels,tires, put everything together and hope for the best?? please help me out especially the guys that have done the complete frame off's time after time project after project....is it easier just to buy,install,and hope for the best, or put together....measusure, order, take apart, install new parts....help me out please....sorry to write so much i just figured it needed some detail. truck is a 68 swb fleetside....fuel injected 350tpi 700r4 98 camaro rear....am using 5x4.75 bolt pattern all around....lookin for a stance pretty close to this truck.. http://www.cardomain.com/ride/2533285 guy used drop spindles and springs.

any help...thanks guys