Hello Kiwi,
A good topic, and one dear to my heart as you will soon see.
I'll be trying to answer your Qs one by one:
1) All the MCA (*gulp*) shells I have seen so far seem to be steel-backed aluminium-tin shells. NO lead bronze, NO running-in layer whatsoever (white metal, Indium, you name it, it's not going to be there). Aluminium shells are commonly used for low- and medium-load engines (petrol and non-supercharged Diesel engines) nowadays, but if you ask me, mainly for reasons of costs. I've been in contact with a very nice chap from Vandervell UK (now owned by Mahle), and he said W*$$*l asked them to produce proper m'cycle bearing shells for them, but then decided against it due to the high manufacturing costs! No more "made (with pride) in the UK" stuff for us...
If you want something good, get a set of shells from SRM, these are proper three-metal bearings (steel back, bronze, nickel barrier and a very thin running-in layer). SRM says they are made by Clevite in the US, a well known name in the world of engine bearings (now also owned by Mahle btw)!
2) Common sense ref bearing clearance is to use 1/1000 of the journal diameter. Anything between 1 to 2 thou will be just fine (I'm using 1.5 usually). 2 thou definitely won't result in knocking or premature wear, an engine with 2 thou bearing clearance and a working lubrication system will run happily for years. Another story is 2 thou of wear on the crank journal (out of round), resulting in a max. clearance of 4 thou and even more with worn shells. This IS going to knock! 2 thou out of round on the journal means it's time for a regrind.
3. Clearance figures apply to all sorts of shells.
4. yup.
The best way is to give them the rods and shells and have the crank ground accordingly to give correct clearance. Have them also check the blind bore on the big ends, rods are known to warp or wear ovally, which has to be fixed first!
Some pics for guidance:
This is an MCA (two-metal) shell, treated with a file. Note only one layer of aluminium-tin alloy and serial number for reference:
SRM shells:
Cheers, Markus