Factory 16×6 versus 16×8 comparison

['68OrangeSunshine]

I use 6x16 white spoke rims on my '68 C/10 Stepside. I changed over from OEM [spec'd in SPID] 17.5 x 5.25 rims w/7.00x17.5 tires. Moved up to 8.00x17.5 in the Mid '70s when 7.00s were NLA. Upgunned to 8R-17.5LT in '80s when radials became available. By the Year 2000, the tire shop told me my OEM 17.5 rims were shot [+250,000] so I got a set of the 16x6 rims and put 235/85/16LTs all around.
I was happy with them for 20+ years, but this April I got side-clipped by a big black sedan Downtown. They centerpunched my Right Rear wheel.
I called all around, looked on Jegs, Summit, Tire Rack etc online. No 6x16 white spoke rims anywhere. I paid a local Wheelwright to true my impacted rim. He charged me $80. While I had the tire dismounted at Dicsount Tires, I noticed a warning sticker inside the rim stating this was a trailer rim and specifically prohibiting the mounting of high speed tires like 235/85/16s. [?!] At this point, I figured 20 years w/o incident proved they were overly concerned.
So I called a tire and rim place in town, and asked for a white spoke Trailer rim 6x16 - 6 log, 5.5'' bolt circle, 3-5/8'' backspaced. Sure, he had one left. I hopped down the next day and grabbed it. This was the 5th rim from the set I had bought from the guy's Dad at the same place, way back then. $68.
NOS but dusty. The rim shop guy's jaw dropped when I let slip the rim was a spare for a 1/2 ton pickup. When I told him I knew all about it, didn't care, and had driven on them for almost 200,000 miles -- he just grinned.
A good friend from work gave me a set of 16x8 aluminum rims he took off a new-to-him '99 4x4 Suburban. I have the intention of mounting tall, skinnier tires on my '71 GMC K/1500 4X4 Jimmy, to replace the 33x12.50x15 meats on 10x15 chromed 8 spoke wheels. 235/75/16s is the plan. I've been successively power washing them, and these rims look fine. [235/85/16s are reccommended only for 6 - 7.5 rims, not 8'' -- so commonality with the pickip tires is out. My '67 K/10 Suburban had 33x12.50x15 tires on 8x15 rims.]
However, I find the aluminum rims are backspaced at 5'' not 3-5/8'' So I may need wheel spacers or bolt-on wheel adapters to use my ''free'' alloy rims. Plus special lugnuts 22mm x 7/16-20. plus 4 adapters [?$] and new tires [+$700].
Getting steep here, just to get better mileage. You can buy a lot of gas with $1000.