If your exhausts are sunk, the only good fix is insert seats. If your machinist cann't or won't guarantee the work (says there isn't room, or says the insert might fall out) take your money and work elsewhere! 2.02/1.60 valves and hardenes seats should fit fine. Also, as for seats coming loose, that is a sure sign of substandard machinework. Think about it, ALL aluminum heads have insert valve seats on the exhausts, and most on the intake. There are millions of cars running around with aluminum heads (and in fact most new cars have warranty periods which are longer than the typical service life of a car built when our Mopars were new. Hardened valve seats and unleaded fuel are a major player in this.)
Most J-heads did not have the induction hardened seats, so 40 years and umpteen thousand miles later your factory seats are probably pretty pounded out. Seat wear is mostly a function of guide wear and high mileage, and not unleaded fuel use, but thats another story. Sure, a larger intake valve will be a suitable fix for the intake. Now, run the numbers for a minute 8 new intake valves, 8 new exhaust valves, 16 guides, 16 valve springs, 16 retainers, 32 split locks, labor to install all of the above including a good 3 angle valve job to include a deep 70-80 degree cut on the intakes (to match the port to the larger valve), hot tank, bead blast, mangnaflux and a surface cut, and you're well past $500 easily. Even if you plan to do it yourself get a quote for labor to gasket match and bowl blend. Just for fun price out new aluminum heads. Something to think about.
