/6 cost

No expert here, but I would think its a fuel thing. Could be just a clogged fuel filter? How low has your fuel in tank been? How long has it been doing this? What (if anything) did you do to it before it started acting like this? Will it idle in park?
No need to search the net on how to fix your car, just search here at FABO.
I paid $200 for a 72 225 with a offy 4bbl intake, holley 650 carb and unknown brand of header. Runs great. Slants are getting harder to find because most folks want a V-8 and just scrap the mighty /'s. If I had room to store and $$ to buy I would get all I can. Good luck with finding the issue.