I took the 454 block to the machine shop yesterday. These things have a propensity for spinning bearings, and this one has. It is getting a caustic bath so it can be meaured. Looks like I have 2 x options if the tunnel can't be saved in its current location:

Machine the caps down 10 thou, and align hone the crank tunnel 5 thou (0.125mm) closer to the camshaft. Then I just buy a 5 thou shorter timing chain set. This shouldn't bother the front and rear seals but not sure what detriment it has to the tranny's centreline. OR

I can buy 20 thou oversie bearings for the front 4 x mains, so get those 4 x journals machined out 20 thou oversize (20 though bigger on the outside of the bearing), and leave the rear main as it is. Problem is you can only buy these oversize bearings in 10 and 20 thou undersize (on the crank journal, ie inside of the bearing). I haven't measured the 427 crank yet but I think it is 10 thou on the rods and standard mains, ground ready to go. It may be 10 thou mains though.

Any thoughts or insights?

I really want to run this block as it was a crate motor, hence there is no pollution gear problems (in NSW i'd have to run 1995 US pollution equipment if it was a production block). It is very hard to find a std bore pre 1972 427 block otherwise and the pistons i'm running are only available in +0.030 and +0.060 (forged L88/ZL-1). I don't want to run a +0.060" engine.