I think hedman makes the hustler for the 351w. The only thing is I think they need a engine plate no motor mounts I could be wrong. The only other thing would be custom.
I think that the Hedman headers you are referring to are actually the Pinto/351 swap headers that require big cuts in the inner fenders and two pipes per side to route through the fenderwells and back under the car. There was also an older header which is no longer in production that routed all 8 pipes under the suspension crossmember...very pretty for wheelstanding, but probably smashed flat on touchdown! Both of these headers will work better for drag racing than for street driving.
The pinto swap 351 and they did have them in 302 headers were hooker. The 8 primary tubes under the crossmember are the hedmans. I am pretty sure you can get all of these from summit the only thing is the hookers for the pinto they need a certain amount before they produce a batch. I was thinking about modding a set and using them in the past. Didnt want to use the headman huslers because of the motor plate and like you said crush crush. This is the hardest thing with these cars headers.
The Heddman 302 headers can be made to fit a 351. I did it. Bought a bunch of misc. bends and reworked them a little. I even reworked them a second time to fit an AOD in the tunnel with a 351w. It is possible. The Swap Set hooker sell requires the moving of the battery adn cutting out the Batt. box and under the brake booster. I did have to bange the area below thwe battery box a little but they fit pretty decent.
I was wondering if a set of shorty headers would fit on the m11 as I am still running the 302 but have installed the 88 5 speed and with the normal headers I found they would not make it past the belhousing and pretty much all the shorty headers I have been looking at shoot out to the sides to quick, I have also thought of going thru the inner fender skirt and custom build a set of headers running into sidepipes as it will be outside of the frame already but seem to be lacking a bit of room by the upper control arm, how far does the header pipes have to stay away from the rubber bushings on control arms? I was also thinking of heat wrapping them too