Your decision should take into account how you use the van. If you're
planning to take long runs with several people in it, you should tear it
down and do it right to avoid getting stranded in Podunk. If you use it to
buy a quart of milk now and then, go cheap.

Another question: how do you know the heads are bad? Maybe it's something
else, hopefully cheaper. I thought the same thing once, only to discover
that the heads etc. were ok.