Exhaust exhaust manifold leak

People pull motors out of cars all the time and leave the transmission in the car. I pulled the 302 out of my Bronco once to replace the rear main seal. I would imagine you will have to remove the hood, I've never worked on a II. Using a cherry picker you should be able to get the engine out. However, with the headers and everything in the way It might be easier just to pull it all out. I would think you could unbolt the headers, your running long tubes right, and then be able to get to the bolts you need to get to. And a friend or two. You'll definitely need extra hands. That's my $0.02.

You can hacksaw the flanges in between the tubes the headers will seal up much better as individual tubes. You just have to be more careful handling them when they are unbolted from the car as they are less rigid than when attached together.

The installed height of a valve spring is only really useful on a new valve spring, and is ultra important in the performance of an engine.
Installed height is calculated to be the height at which a particular NEW valve spring has its designed seat tension and also will not coil bind with its intended use cam at full lift.

All of this changes with a "used" spring.

A spring, once removed, which measures less than it's "free height" specified range when new, has lost tension and therefore cannot be used at the recommended installed height. This is where the shims come in for a stock non-high performance rebuild. On a stock engine with low lift there is plenty of extra space in between the coils, so using a shim underneath restores the correct spring pressure (at least for a while) and maintains clearance for coil bind.This is attained at a "less than" specified installed height. This works fine on stock engines (grocery getters) and stock usage (no high revs). To do this correctly you need a valve spring tension tool to see what height is required for the seat pressure needed for the application.

In a high performance engine this is a no-no because there is less coil bind clearance to do this, and more chance for bind. Any more than minor shimming means you either do not have the correct spring, or its worn beyond usage, or some other problem. New springs are the ticket if you have less free height range than listed for that spring. If you have a valve spring tension tool you can evaluate springs correctly, other wise it is simply a guess. All high performance springs even when new should be checked on a valve spring tension tool to ascertain whether they match their listed specs or not. I have seen many "brand new" sets with bad or incorrect springs in them, as well as new heads with mis-matched springs on them. I personally never trust any springs I don't measure anymore, and I have never wiped out a cam even in the era of flat tappet cam death.

For a country-boy back yard method you can use a decent quality bathroom scale and a c clamp and slide calipers, but this is something that is better done on proper equipment.