Timing

OK. I'll start there and see what happens. Thanks.

you need to do the heads first you may get away with lapping the head
also check the bores for scuffs

then when you assemble it back up peg it mark the flywheel at 8* and then make the 2nd mark then watch to see what the DG gives you when its stopped advancing.

you can use tipex to mark the flywheel teeth

i,m prob going to get slaughter here --but i would check the head bolts for the correct tourque first before a stripdown and adjust the valve clearances if the bolts need tightening
that may do the trick

Did anybody mention a compression test first

Ajay it might do the trick. ken has suggested a re torque of the heads too.
Viking what would you be looking for with a comp test ?

Compression

Yes, any compression would be a positive start! But can you be more specific?

To measure if possible, how much compression is lost between the cylinder and the head. If the engine is farting (between head and cylinder) doesn't that mean air escaping.

Also before ANY stripping down a compression test should be done, to get a picture of what one is looking at and dealing with (valve (seats and guides) piston and barrels etc).

Viking,
normally that's the best procedure, however these comments about Smiffy's engine suggest that there's not much wrong with it, apart from leaky head/barrel joint(s).
Car goes like a train - 75mph easily.
No smoke.
Good compression.
Starts 1st time every time. But now it's smelly.

There's no chance of detecting such leakage with a compression test, which would only subject the joints to between 150 & 175 psi.
The problem is worst at WOT under load, when the instantaneous cylinder pressure will be more like 700 to 850 psi...

ken