B_RAD69

I have a 6.0 Silverado with the lq4 iron block, planning to start with an exhaust, and move on to different heads/ cam and valvrtrain. For the exhaust is like to go with Texas speed headers into 2.5 inch pipe into an x pipe into more 2.5 inch into 2 black widow venom 250 mufflers and then just go out the back, true dual style. I'm not gonna do the fab part as I'm a newbie to welding. I'm wondering what size inlets the mufflers and x pipe should be, since butt welding exhausts isn't that good of an idea and I want to do this right. If I have 2.5 inch pipe, should I get mufflers and an x pipe with 2.5 inch inlets and adapters that go over the exhaust and scale down to 2 inch or something else I'm not thinking of. Any advice helps here.