Well man, your best bet, to get "headers" is either TTi or I'd even say Schumacher, Tri-Y (they're GREAT!) The Tri-Y headers would fit ANYTHING as long as you change the heads that 413 came with, the industrial 413, has an odd-ball head, low compression pull yer freakin house down torque..... BUT you can get more out of that block then it has right now as far as HP goes....
The 440 heads, STAY AWAY from the 516's RB heads (too low compression!) 915 or 906 heads be your best choices, OR you can go aftermarket heads topo, (MOST of the aftermarket heads will bolt right up too, and those if it were me and I had the cash? I'd go Edelbrock High Performance 440 heads, closed chambered heads (remember the closed chamber heads raise your compression, and in that engine as it, I bet its around 8 to 1, maybe even lower (I can't remember) BUT I know its REALLY low for a stock street engine used in a camper. my '67 Power Wagon W200 has a 383 built much the same way as that 413, but its Military order so.... Mine however, is stock as ordered I've not changed anything on it.... But it would pull my house down if I had a chain long enough to wrap around it LOL I thought about what your doing and let me tell ya, the heads and intake you have on that 413 were built to last, and it was made for down right torque power....
You go an build that 413, the intake and heads it came with hae to go.... the intake bolts up to the heads with a one-off bolt pattern, just like my 383. Your 413 is a RB block, and my 383 is a B block, so I couldn't use the intake you have but the heads I could, (bolt pattern should be the same thing, but angle in which the intake bolts to the heads would be different due to the 2 blocks different deck height. Thats why, you can't use just "anything" and try to piece it all back together, you really need to rebuild the whole top end of that 413 to do it right.....
And if it were me, I'd give that block a good "once over", if your going this far with it, a total look over would not hurt! Check ALL the oil passages, (clean them out if needed,) and then check the bottom end, oil pick up, CLEAN IT OUT, all new seals, and check the crank bearings.... as well as the main seals specially the rear one! Do you have a garage or machine shop close by? I'd strip that whole block and have it sonic'd too, to make sure its "solid" and worth your time and money.... I know several people that didn't and paid dearly in the end....