As far as I know, Tony "Halco" is no longer with us.
These guys (The Probike Centre, Wolverhampton, West Midlands, 01902 401335)
have an engine for sale on eBay which should interest you........
http://cgi.ebay.co.uk/Yamaha-XS650-XS-650-Engine-840cc-Conversion-Halco-/200575179286?pt=UK_Motorcycle_Parts&hash=item2eb3365a16They (The Probike Centre) say:
Due to a cancelled order, redunancy we were told, this is a rare opportunity to purchase this XS650 engine which has been proffessionally converted to 840cc by ourselves (XS enthuiasts) to "Halco Tuning" (the lateTony Halls specifications).
The engine has been entirely stripped (a must for this type of conversion) it has had the top engine case machined out to accomodate the new larger liners and barrels, it has new pistons, new timing chain and tensioners both pivoting and solid, new camshaft bearings, new sump gauze filter, new crank seals pushrod seal, cam seals, plus all new gaskets throughout. it has a new 7 plate clutch conversion and heavy duty springs ( a must for handling the extra power and torque. It also comes with generator stator and rotor, carb manifold rubbers, kick start, the cylinder head has been stripped mildly ported and polished, the valves and seats re-cut and lapped in - see pics.
The engine cases have been vapor blasted and eched then painted with proffessional satin black case paint, same with head and barrels which then had the edges of the fins milled. the clutch and generator covers and tappet windows have have been proffessionally polished and an original Halco Tuning generator cover fitted.
All you need are carbs, and an ignition system and oil, we would advise a Boyer Bransden system they work very well with this conversion, we can supply and install at an extra cost, or we can fit a points system for no additional costs.
This conversion costs over £850.... for machining and piston costs alone! SOLD for £1850If you're just interested in building one yourself and it being 800+cc, then its back to Heiden (Europe's "Mikes XS" dealership) as they do an 880 kit off the shelf, but the donor bike has to be the right type (447 or 533, differnet con rod lengths I think??).
It also mean opening up the crankcase mouths.
http://www.xs650.biz/p/28/1423/home