O.K., here goes another opinion from the peanut gallery
: first, before any disassembly, I would do a compression and more importantly, a leak-down test, in an attempt to establish a somewhat better understanding of the current condition of the engine. With the leak-down test one may establish how great and from where the bulk of any cylinder leakage is emanating from, thereby determining whether just pulling the heads alone is of value in the overall situation.
As far as recommendations of specific processes in the rebuilding machine work, that should be left to the machine shop holding these applicable components, as it would require observation/inspection of their condition.
Not to be at odds with anyone, but since it was mentioned, I prefer to use bronze guide liners (vs. complete guides) in restoration type (old car, "cruisers") guide repairs. This process consists of boring the valve guide bore +.060"+/- pressing a .030" wall bronze sleeve (cut to length), an expanding process, reaming and or honing to size; this removes less original parent material from the cylinder head, leading to less tendency for valve face displacement and is indefinitely replaceable in the future with no further machining of the cast iron. Oh, and it costs less!
As far as hardened exhaust seats, one should look at the existing condition of the cylinder heads. If the seats are "beat-out" then replacement seats it is, but if they're not sunk badly, then for the "cruiser" or show car, I generally agree (Tbird6), that incurring the cost, and, realizing that the manufacture did not intend such a process being executed, therefor did not intentionally provide excess material within the casting for such, and therefor realizing (and experiencing) that not all cylinder heads survive such efforts, it just ain't worth it,..... just to do it.
And, for my other two cents: NOOOO! do not remove and replace the 430 MEL with something else!