Its certainly easier to get them out with the rockers off.

Yes, 100%.

Some years ago I replaced the worn out 4G63 in my 89 Vista with rebuilt
4G64B from a Hyundai Sonata. Actually I did it twice, as the first 4G64
lasted 15 months before a %&*@## jet valve burned out and jammed, causing
the rocker to break, which then caused a valve to drop into the cylinder.
The piston came back up and stuck the valve back into the head, but not in
the hole it came out of ....

I used the Sonata intake and injectors, and the Vista exhaust manifold
(Sonata won't fit clear the radiator). The Sonata ECU is a direct, plug-in
replacement, though I recall I switched the ECU board in the case so it
would bolt in easier. Everything else is direct bolt up replacement. If your
88 has a carb rather than fuel injection, you'll have to do some extra
wiring.

The 4G64 SOHC 8V is 2354cc (hence marketroids can call it a 2.4L) with a
much longer stroke that provides lots of torque, but also limits the engine
breathing to about 5500 rpm. If you are going to do a swap, you might
consider the following:

a) swap the G63B SOHC 8v with a 4G63B DOHC 16v  (Eagle Talon, 93 Sonata,
Eagle 2000 GTX). Its a better engine and is more lively than the 4G64 SOHC
8v. In fact the 92 Sonata had the 2.4L 4G64, and the 93-95 had the 2.0L 4G63
DOHC and performed better. The DOHC will fit in the Vista. You'll have to
sort out a new front pipe as the exhaust manifold flange is different.
Likely a Talon front pipe can be adapted to fit.

b) if you really want 2.4L, then the 93-95 4G64 SOHC 16v (eg from a Summit
wagon) will fit, its a better engine than the 4G64 SOHC 8v, and does not
have the %#$@ jet valves. You will have to do some fiddling with intake
parts, but the sensors are more or less the same, just in different
packaging. PROBABLY, you can connect up the existing bits and it would work.
I'm not sure if the ECU has the same connections and connectors as the 4G63.
Its likely quite a bit more work than swapping the 4G64 SOHC 8v.

Whatever engine you choose, it would make sense to rebuild it as necessary
before installation.

Stewart DIBBS

You will have to at least loosen the rocker shaft assembly anyway even if
you slide the rocker over.
Removing the shaft assembly is no big deal.
Just put the tips of some latex gloves over the rocker ends so the lifters
don't fall out.

Rich