First up, make sure you know what you've got, -2.5 or 3-litre, it doesn't really matter as they're essentially the same, but it will help if you know what you're starting with. Providing you're going for a strip down, retap the head-bolt and water pump bolt holes us ing a plug tap, and make sure the oil drillings are flushed out.
Clean the block before and after you've had any machining work done. Martin, from V6 specialist Car Clinic, reckons you should steer clear of cross-drilling, as it reduces oil flow to the big ends. Aside from boring, machining work is limited to a bit of chamfering -firstly the bottom of the bores, to stop the piston shaving off the oil on the compression stroke. You can also clean and chamfer the oil filter hole. This gives a better return to the block.
Always make sure you replace the oil pump spindle, due to the corners rounding off. Get one that's been heat treated - it'll be black on the ends. All original Ford items are heat treated.
Only cover your core plugs with a screw plate if it's for racing. Martin does this by tapping three holes around the core plug and filling the cavity between the plate and plug with mastic - this could potentially save an engine in a race situation.
For the ultimate, you could always go for one of Car Clinic's 3.4-litre conversions using genuine Ford OE parts. .
Martin reckons a particular problem with the Essex is the land in-between the rings breaking up. This is virtually undetectable until you remove the rings - it can then break free. Because most engines have been rebuilt by now, they may already have over-sized performance pistons - these can be particularly weak. So don't buy rings until you've checked everything.Standard-type pistons with a 8.9, 9.5 or 9.8:1 compression ratio are still available from Car Clinic, or it can supply new, lighter than standard pistons with a 9.5:1 compression ratio. These are really only needed for racing use, and the engine must be rebalanced after fitment. Car Clinic also likes to do a bit of piston skirt grooving, helping oil retention on the lower piston.