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Wow. I didn't realize the BS was that deep.
So they could be either metal, eh?
And a replacement that is 3.75 BS will add an inch sticking out. Hum.

Yeah it will stick out an inch more.
I'm running 15x8 with 3.625 backspacing and they stick out over 2" more than stock. (1" wider plus 1.125" backspacing difference).
1" will be fine, not a big deal. will look alittle more aggressive. DO you have mud flaps? I find the farther the wheels stick out, the faster your truck gets dirty LOL...

Mine:
[Linked Image]

89 4Runner
3" BL, M/T locks, 33"bfg mt, bilstein, Kayline, tubebumper, toyotafiberglass panels
TBI: Elocker,3.4 w/ORS,b+b,S2Sstg2cams,arias pistons,P+P intake,TRDs/c,URDpullies+7th,downey headers,MAPECU2,WEGO WB, SupraMAF,walboro255,stg4clutch, EPaOo2 sim