OK, went to see my engine in intensive care.
Its now dis-assembled.
The "noisy tappet" was the bolt that holds one of the rocker shafts in had broken (it had been welded previously too!).
The shaft had worked its way sideways and the rocker started to be at an angle as the shaft had moved. As to whether or not it has caused the rocker shaft casing to be oval or not we cannot tell at this time, until the head is stripped. Fingers crossed.
The angled rocker has damaged the camshaft.
Shims on the end of the camshaft were missing. The cam chain sprocket has marks were it has been moving, and there is a pin that was on its last legs.
It has had one new (or replacement, probably secondhand) barrel in the past. This barrel is in OK condition, but the other 5 have hatching marks and need replacing, so its 6 new (or good used) barrels and pistons.
I need a new (or used) camshaft.
Some of the nuts and washers in the engine are non standard and really bodged. some studs replaced, others not, wrong nuts fitted. It grieves me that someone has done a top end rebuild and not bothered to do it right. I will be going through the receipts for the last 10 years to see who might've done this, but as the car is 21 years old it may have been done a long time ago.
The bearing shells for the oil pump are worn through to the copper, but the indy says these can wear through at about 60,000 miles anyway.
The conrods look in good order, so new bolts, shells, polish crankshaft, and strip down the oil pump to check it but I am told these are normally pretty good so it should be OK.
The good news is that everything is fixable. I have decided against 3.8 barrels and pistons, as because my car was in such poor condition, just making it into a properly built engine will be a dramatic improvement anyway.
Timing chains look in excellend condition. I'm tempted to replace them anyway. I will wait for pricing. Any thoughts? Obviously its easy to say change them, but where do you draw the line?
Tim-ware is knackered, so will all be replaced. It has been welded, siliconed and had holes cut into it previously.
I will have more idea of costs when everything is priced up.
Thanks to SteveJC I now have a decat pipe to go with the existing G-pipe, and the primary silencer isn't standard either. My indy says he doesn't know what it is, but its a sports pipe of some description.
I reckon I will have to got through all this cars history records and find out what has really happened to it. However its going to have a better quality of life from now on.