This is not a difficult job but may give that impression
when described in some detail.

Presuming you are going to use the common and plentiful
GM single wire alternator:

Remove the generator and the manifold mount mounting
bracket.

Modify the manifold mounting bracket for the alternator
pulley belt alignment. This means drilling new stud hole
locations and probably removing a corner of the "ears" so
that the alternator is allowed to swing vertically for belt
adjustment. Turn it upside down for new the hole placements
and then you can always reverse it again to use a generator
if/when you have a reason to undo this.
     With correct belt alignment, the BACK end of the
ALTERNATOR will end up with about 1/4" clearance
to the FRONT end of the VALVE COVER.  I find it
helpful to lay a straight edge along the other pulley front
surfaces to achieve belt alignment quickly and without eyeball
estimates. This method also checks the plane alignment of the
alternator pulley itself.

Install a piece of threaded rod through the pivot holes in the
mounting bracket.  This is for the new  alternator to swing/
pivot on. Nuts and lock washers on this rod will permit some
belt alignment adjustment however this adjustment will be limited
because of where the ears of the bracket are located.  So try to
get the location close the first time when you are choosing the
new hole locations.

Modify the curved alternator  ( belt adjustment )  arm:
Bend it and  grind some alternator case clearance on the
lower curved edge of the arm.

After carefully noting which wires went to which regulator
terminal
marking.....................................................................
.......
remove the regulator and the two wires that connected the
regulator to the generator.
    The remaining ( usually largest ) wire that originally
went to the "B" or "battery" terminal can now be spliced
and extended to the large stud terminal on the back of the
alternator.
   ( If,  instead,  you decide to run a wire directly
to the battery or starter solenoid terminal instead, the
ammeter will not be in the circuit and will not work. )
By using a screw/nut with spade lugs to do the splice you can
always reverse it again to use a generator if/when you have a
reason to undo this.
Obviously you should insulate this splice from touching any
other metal.

This same basic procedure applies to using the two wire GM
alternator with a few additions which I can provide if needed.
These two wire alternators have been a little more common and
cheaper to buy.

If there is excessive alternator vibration when you test run it
the ears of the new alternator will not last long. The vibration
may be a result of belt misalignment. There is a possibility of
modifying an original GM upper arm and using that to provide
greater support but I have not pursued that avenue as vibration
can usually be eliminated by adjustment.

When buying the alternator the lower rated ( 62amp? ) is usually
adequate unless you have extra power needs. A 100 amp alternator
can be used by those who feel it is more manly and don't want
feelings of inadequacy.

Lark Parker