Jeep 258 Conversion

[Mike Comai]

I am new to the list as well.  I have recently been looking into an
upgrade for my AMC 258 I6.  It has become clear to me that the only way to
economicly do it is to do it myself.  I have looked into Howell's kit and
it looks pretty good (aside from the $1k pricetag).  I called up and tried
to order just the GM -> AMC intake adapter and they would only sell it to
me with their "harness" and PROM.  Here is my 1st question - They charge
$350 for their harness and I asked them why it was so expensive they said
it was due to the filter for the RPM sensor.  What is the signal needed at
the computer and what kind of conditioning would I have to do to the
signal off the negative side of the coil?

I also plan on getting an adapter machined (unless there is a better way?) 
but I don't know how crucial the design is.  My thought was to take the
shop the old Carb and the new TBI and have him machine me a 1" thick
plate, putting recessed holes for the plate to manifold mount bolts and
threaded holes for the TBI to plate mounts.  How crucial is it to taper
the TBI hole to the manifold opening?  Are sharp edges ok or does it need
to be smooth? 

Last question is about the PROM.  I will probably eventually write my own
prom but initially I plan on using the prom from a 4.3L GM donor (post
'87).  Will it adapt to the 4.2L AMC motor ok? 

I would appreciate any help and suggestions for improving my approach as
this is a new thing for me.

Mike Comai
1979 Jeep CJ-5