exhaust manifold interchange

[kljfamily]

Hello group!

65 c10 stepside
installed a motor I found off of craigslist from a 1978 c10. Its a 250.

The exhaust manifold is an odd size. I keep ordering the exhaust flange to hook up the exhaust(walker 31883) but it comes in with holes spaced 3" apart and this particular manifold has the bolt spacing at 2-3/4. I've tried ordering the flange from a variety of sources but it comes back wrong each time. I think this may have to do with the 78 having the integrated or non integrated head. this particular one is non-integrated.

Here is the motor info:
The intake is a gm 343303 43 and exhaust is a gm504
motor: con2 f168 377127 gm 86 then behind distributor f0622tar

I took a look at the walker exhaust system website for the 78 and it shows two options for the 250 in that year. The first has the collar 31183 and then the second doesn't show a collar. I'm assuming possibly the collar was built into the exhaust pipe.

My question is this:
Can I use the exhaust manifold from the 65 230 engine I have (Blown engine) and then just hook up the stock exhaust easy.....or is there something Im missing on this 78 engine?

I just finished up the body work and bed so I'm broke and I know I should probably just take to midas and have them custom fit it but I'd like the finish up this ground up restoration myself and I have done every part of it so far.