The kid who I bought my truck off of did a real hokey joke job with the exhaust, stock downpipe to the end of the cab, then a 4 inch adapter to some flexibend tube up to a giant bed stack. Kids these days.. Anyways I am redoing the whole exhaust to 4 inch turbo back, but need a little help. I have a 1989 with a stock turbo, when I look at Downpipes there are different flange options. So which one do I need?

 

You want the basic/stock v-band style. Its 2.5" or 3" depending who you talk to. The stock pipe is 3", but its smaller at the v-band coupling.

You can see my 'stock' fabricated flange with a DE 4" kit for the 'stock' turbo here:
https://www.dieseltruckresource.com/...flange-299516/