I saw a post in the wanted section for a factory tach. Here's a sugestion I have. Dakota Digital makes a pretty reliable translator unit where you can run any gasser tach to it's output. I know OEM looks better but spending $300 imho is nuts. I did this on a GM diesel where there was no tach option for years.
here's the link to the product.....
http://www.dakotadigital.com/index.cfm/ ... prd129.htm
here's the link with pics where a ford tach sensor was grafted into a 6bt.
my link for Dakota Digital is post #21.
http://www.oilburners.net/forums/showthread.php?t=24463
mods-
if it is illegal to link to another BB, please delete the second link and LMK via PM.