other possable ways of "fixing" the problem without a lot of brain damage are to use the vacuum advance port for the distributor to also supply the trans. or get a vacuum canister like many of the GM and Ford cars use on thier cruise controll systems, these look something like a juice can with vacuum fittings on them, built into them is a one way valve to allow vacuum to be stored and allow enough to be there when it is needed,
you can probably get one at a local wrecker for next to nothing. that would save you the time and expense of modifying or changing the trans.