Doesn't it have a huge heater box where the LA distributor would go? I be a 383 with logs would drop right in.
Probably would have to go with fender well headers.SB will be simple; RB will be difficult, but possible. One option you did not ask about is BB, which would be easier than RB and can be built to the same HP as RB. Your most difficult part for the RB and BB is header selection, it doesn't exist; custom made headers will be a must.