I've checked into this and found the aluminum block saves less than 100 lbs in weight in the front.
A couple suggestions- I would seriously consider talking to a couple of the engine builders on this site- Mike Forte comes to mind as well as several others that have great references on this site. They should be able to steer you in the right direction so you get the right parts that will work together to make a great, well mannered engine for your purposes.
This is only my recipe, but I liked it-
Seasoned 351W block- 74 casting.
Vic Jr. heads- cheaper than the AFP and come with better hardware.
Comp Pro Magnum roller rockers
Rotating assembly from Brian at AD Performance in Seattle. Great service and very knowledgeable. Easy to work with and good prices. If it were me, I would go with a 408 instead of the 427, given all of the back and forth on the pros and cons of the 427 in a 351W block. Or go with a big bore Dart block and do whatever turns your crank.
Cam- I went with a Comp XE 294, which has a very lumpy sound and great response. I would have to find the cam card to see if it fits your profile. Timing chain can be ordered with the cam from Comp Cams as a kit with everything you need- lifters, chains, gears, cam, lube, etc....
I used a Canton road race pan on my car and very happy with it. It sealed up perfectly with the mounting instructions I got from Gordon Levy.
Clutch- for your purposes, I'm not sure I see any gain in going with a lightweight clutch set up. A nice Ram would probably work great and be easier to live with for street driving. Same with the flywheel- any good SFI flywheel will work fine for your purposes and save you money for other things.
Pulley set ups are a crap shoot. I went this route on my 393 and it took me quite a while to find all the right parts to make the pulleys all work and line up. Again, someone like Mike Forte can help you with this and recommend the right pieces to make it all work.
Can't help you with the injection system- I'm pretty much a carb guy. I may be getting too old to start learning new systems now.....
One last note- if it were me I would be sorely tempted to find an old 289 and build that up to put in the Kirkham. Performance parts are still available pretty readily and they still make great horsepower.
Good luck with the build.
Bob