I've not done the bbc/'61 c10 swap. I did do the bbc/'66 c10 though. If you locate a '61 v8 bell housing that'll bolt up to the bbc & your stock rear motor mounts (I believe). All other related parts from the small block should work too. IE: clutch linkage (hyd clutch in your case, I think). Trans should bolt right up. Stock replacement v8 Starter should work.
Biggest issue will be getting the right flywheel. 454's (as you probably know) use a external balance system thru the flywheel & the harmonic balancer. In my case, I had a bellhousing that worked with a 168 tooth flywheel. So I checked out a stock replacement 454 flywheel for a '92 one ton truck engine like the one I have & it was for a168 tooth ring gear and I guessed that the balance weight would be correct. In my case, the auto mactic flex plate that my engine came with had the correct balance weight stamped on it, the new replacement flywheel had the same # stamped on it. In other words, make sure your flywheel is the correct balance weight & the correct ringgear size.
The firewall will need a little help from a 2lb hammer. I set my engine in place, as close as possible, and marked it with chalk so I'd know exactly where & how much to "massage" it. It's a small amount & not even noticable, imo. After setting engine in place after working out the front & rear mtr mounts, make sure the valve covers can be removed. If not, the firewall needs a little more help from the 2lb hammer. Also, decide up front if you're using stock valve covers or Tall covers like for a high lift cam with roller rockers. It'll make a difference on how much firewall clearance you need.
For my swap, I used '66 Corvette 427 exhaust manifolds. The frame needed a little clearance work. You'll have to figure out what'll work best for your swap.
Don't know what to tell you about the front engine mounts. You're on your own there. On my '66, I used the original 6 cyl f rame mounts with stock 66 engine mounts . I modified the frame mounts a litle so my carb would sit a level as possible.
That's about all I've got, but it should be enough to get you started. Good luck with the project.
