351w Swap Help (headers)

Ditch the stock K member.... contact @Sharad for a new UPR k member and alleviate a lot of the interference issues you are talking about. Is there a reason you require a stock k member? Kooks has a lot of options as far as primary tube size goes, be forewarned that they will hang low... Ask me how I know that. I have used Accufab headers as well in the past for swap like this and had decent success. Hooker makes a 2" primary 3.5" collector header for this application too but I can not attest to how well they do or don't fit.
What is the compression of the motor? Typically on the blower/turbo applications or N/A applications with compression 10:1 or lower a stock 93 mini starter will work just fine. If you have a higher compression motor I would recommend a power-master mini starter, best bet is to call them and talk about specifics. They have a few different options depending on the specifics of your build and can help you choose the appropriate starter the first time.

i have the hookers 6228s for my new highport motor but im not sure how they fit with the brodix heads... you might need to order a set from kooks who seems to make a header for just about every header combo.

and +1 on calling @Sharad and getting a K member from him. so much more room to work at that point. we actually ran a stock mini starter from advance auto on the nitrous motor for a long time which was 450" and 14:1

I had the hookers but they hit my firewall. (no issues with the UPR k-member, obviously) I ended up building custom headers for my 9.5" 351 with High Ports.