Classic/Antique Car Repair: 1966 Mustang, valve seals, chevy guy

Question
Hi Roger,

I know you are a Chevy guy but maybe you can help with at least the second half of my question....thanks
I have a 66 conv. I bought 21yrs ago. I put some money into the car and
had the body repaired and painted about 12 years ago. It has held up
well over the years(no rot so far) but I never did the bottom. The car
needs boxes, rails etc. My first question is what kind of money (rough
estimate/range) am I looking at to complete all the necessary underneath
issues assuming everything needs to be updated.
There are a couple of places in Ct that do nothing but Mustangs but
have no idea what would be fair.
Second question concerns the engine. It has the small 289 CI. I
replaced the two barrel with a four barrel holly and used the manifold from a
1985-86 301 mustang. Problem is, every 500 miles or so I need to remove
and clean the plugs. Four of the plugs(not all on the same bank)
totally foul with carbon (don't think it is rings). Is there something
different about the manifolds that would cause that to happen. I will be
rebulding the engine within a year and don,t want to put it back on if it causing the problem.

Answer
Mike; I not shure what you mean you need for under neeth, but if you have to change the plugs every 500 you might need some head work or valve seals, take a comp. test and see what psi you get out of the cylds. it could be springs,valves,or seals, oe the rings could be going to. if the body is in good shape it is worth fixing up as it will be worth a few thousand easy when done.it could even be the wires? or cap . but mostly the valve seals....>><><