These are my thoughts, which are simply a remix of the above.
Do what Peter says first (chunks o' metal).
I think the plugs are 17mm female allen sockets. Buy a 1/2 inch drive allen socket. I remember buying a hefty long handled 17MM wrench at an industrial supply place in Houston in the 90's. Bummer is, over time the 17MM socket holes can get beat up if reused and the 17mm allen socket can be used with an extension (or two) from outside the wheel well (top sealing plug) and you can push against the ratchet to maintain the bite where the fastener meets the tool. YMMV but that's what I found.
If you find chunks of stuff, full stop. Time for a refresh. If no chunks, craig245's comments are a worthy effort especially if you find wear in the parts he is mentioning
Skip adding a short shifter for now as they do beat on synchros a bit more than the long throw shifter.
Given you are in Houston, there are enough Pelicans around that wrench. With an offering of beer and even a modest amount of cash (no 1099's
) , you may find your new best friend who will help you pull the engine and split the trans.
Whatever KTL is speaking of regarding beefing stuff up, Matt Monson (member here) can do.
Cost to UPS ship a 915 is around $125 each way. There is also a shop in west Houston, past Katy, that is highly regarded. Folks here will know.
Mayo in Dallas is also an option, but I feel Matt knows more about fussing with the synchros and dog teeth to alleviate any "break in" time for smooth operation right out of the box. Something to do with back-cutting something that does not require the synchros to wear some before smooth operation.
After all this wind, and given I know the same amount as craig245 (i.e., limited experience), this info is worth what you paid for it.
I spent $2,500 for Mayo to do mine. The basic tear down and re-ssembly is favorably cheap (under or at $1K) if you drop the trans off.