Hi Graham, did reply to this late last night but went back a page without copying and lost it all!
It's looking good – not long now before that first run I think you'll find that the washers under the capheads aren't really necessary though – I don't ever recall any engine using them.
Sourcing long 6BA SHCS could prove an issue but cheese heads would be fine – again that's what virtually all similar sized engines of the period used but even there you may find it a problem. I have similar issues with 5BA so turn mine from 6mm En1a. I put a small centre in the end for support and make the thread longer than required turning the centre off and reducing to the correct length after.
'Cast in cast' is okay from a piston/liner combination of metals point of view but it does make for some messy exhaust residue. The initial seal usually reduces a little before the surfaces beds in too. I have just rebuilt a 5cc Miles Special for a friend which had a cast liner and piston. Relapped the liner and made a new piston. Once run that initial compression eased a tad though the seal is still good. Personally – for a basic home built I would not move away from a cast piston in an En1a Liner – a good combination of metals with exccellent abillity to create a very good piston/liner seal.
I don't think you have too much to fear about using your Myford for lapping if you ensure the bedways are well covered and the saddle pushed well back out of the way. Never seen that as an issue on mine on this op.
Looking forwards to seeing it run
Hope it all goes as well as it has to date
Regards – Tug
Edited By Ramon Wilson on 13/12/2019 11:46:45