Singlespeed MTB question: chainline related
 

So I have an old 90's rigid-frame geared MTB that I am converting to a Singlespeed cruiser bike.

The chain stays are so wide however that I am having trouble fitting a larger chainring on the bike (even with single-speed MTB cranks.) I want to use a 48 or 50t chainring but it hits the chain stay when I tighten the bb. (I guess thats why most SS MTB cranks are no bigger than 32t.)

I noticed that some cranks like TruVativ Holzfeller and Hussefelt are available with 2 chainline options: 51mm and 56mm. The two options are for standard MTB rear hubs and extra wide rear hubs. I am using a cog and spacers on a standard hub shell. 51mm.

My question is: Can I use the BB with the 56mm chainline on a standard MTB BB?
and just adjust the cog location with the spacers or is 56mm too wide for a standard MTB rear hub?

Anyone know what I am talking about? I would appreciate any help? Thanks.

Curious, why do you want a 50t chainring on a cruiser style mountain bike?

What gear are you trying to push? You can probably push something similar with a different rear cog.

Its a MTB frame but will get only road use. Thats what I worked out to establish the gain ratio I want. (No hills to speak of around here) And I already have a larger cog on the bike and prefer the larger size to maintain less wear. Either way, I would need a tiny cog that is too small to fit on a spline to get the gain ratio I want with a typ. SS MTB chainring.

I tried the Sram/truvativ GXP setup but the one piece spindle does not allow adjustment the chainline. I saw that the howitzer comes in 2 chain lines and still has external bearings. (which I like and have tools for installing)