The following applies only to RTV type rubber such as that sold by
hobby shops or sculptor stores.

I tried making Ampico rubber mounting blocks and some of the ones
I made worked out great while some did not.  I no longer offer them
but I can give some advice.

The rubber should not be mold-making rubber such as Dow 310 because
the shelf life after the rubber has cured is about ten years.  The
hardest mold making rubber used to make molds is usually too soft.
The original rubber seems to have a durometer hardness of 80, or at
least the rubber I used was 80, to support the weight of the motor.

You will need a mold to form your rubber mounting blocks.  It must be
slick or else the rubber will stick to it, making a mess.  A really
nice mold made from aluminum on a milling machine works great.  You
should have a mold that can be immediately placed into a vacuum chamber
to pull the air out of the rubber to avoid the little bubbles.

Buy more rubber than you think you will need as the first couple
attempts will usually fail.  In my case the local humidity was too high
or little air bubbles formed.  The humidity needs to be 60% or below.

The preceding applies only to RTV type rubber such as that sold by
hobby shops or sculptor stores.

Don Teach