i hear ya on the notching the cross member..basically what im gonna do is cut an area out...make a little like box going up on an angle so i can run the pipe up...and im also gonna gusset it and run other pieces off the steel box i make just to reinforce it...i have a good amount of 1/4 inch steel laying around so im gonna go for it and try to take pics...also where did you get your fenderwell exit headers and how much were they...i may even consider going that route
I only mention it because years ago I was on a trail ride with a medium-sized group of guys and actually watched a guy with a nice F250 take a bad hop into a tree. HE had notched his crossmember for header clearance and the whole nose just folded right up from the passenger side. The hood looked like a tent and the engine dropped at *least* 4 inches when one of the perches collapsed. It took ALL of us (something like 7 or 8 trucks) two full days to drag the thing back down to the trailhead and everybody stopped having fun just as soon as it happened. A really nice trail rig became a parts truck in an instant.
I didn't feel too bad about a single body-mount but a crossmember ? I'd do everything I could to reinforce it after taking a chunk out of it like that but it sounds like you're already on the same sheet of music.
My fenderwells came from L&L in Texas but they were for a 460 swap. I've actually bought 3 sets of these headers from them and love the things. I just did a quick search though and couldn't find a single fenderwell header for a stock 351/400 truck. It used to be that ****** has a set but I didn't search their site to see if they still offered them. L&L originally sold Doug Thorley headers and I think they're still the same even after Thorley sold the rights and had his name 'jacked. I believe these days he's forced to sell headers under the name "Doug's Headers". I did a search and "Doug Thorley's" are still sold and so are "Doug's headers" so I don't think he ever got the rights back to use his own name on his own product, poor bastard.
Anyways, if you've got or want a 460 then you're cool because L&L has them and if not then you've got some searching to do or you'll need to just have a set bent up. I've actually gone the custom fenderwell route and it cost me just shy of $750, which when you compare that to the $580 L&L wants and add the shipping I guess it's in the same ballpark. Sorry to be so longwinded but that's about as much as I can tell you & I hope you find something usefull in the ramblings.