I started doing this late November, well not exactly. I was trying to create a (non-bogo) conlang out of Oscan by having a pocket of it survive somewhere. The first and biggest problem I encountered was the dearth of information.
Here is a table of the morphology that I could pluck from various old grammars. I think quite a few forms are conjecture on my part. Feel free, anyone who knows anything about Oscan or Umbrian, to comment or make suggestions here or in a pm. Any help would be greatly appreciated! 

My next big obstacle is vocabulary, but hopefully I can borrow a lot of vocabulary from probably Greek and Latin and make up the rest based on Umbrian or Latin words.

I did briefly consider the approach that you mention ie just replacing Latin with Oscan. 


> On 14/01/2014, at 8:49 pm, Siva Kalyan <[log in to unmask]> wrote:
> By extension, one could even take a different Italic language¡ªOscan, say, or Faliscan¡ªand imagine what would have happened if they (rather than the Latians) had conquered everyone else, by (bogolang alert!) applying all the Romance sound changes to it!  
> Siva
> Sent with Mail Pilot  
>> On 14 Jan 2014 18:38:08, R A Brown <[log in to unmask]> wrote: On 14/01/2014 05:47, Nathan Klassen wrote:
>> Following the discussions in the last few weeks about the
>> disputedly named "bogolangs" and romance langs in
>> general, I had an idea for taking the romlanging in a
>> different direction: What would develop in a situation
>> where speakers of Old (pre-Classical) Latin were isolated
> How old? Way back in the 7th century BC when we find
> "Manios med fhefheked Numasioi" (Manius made me for Numerius)?
>> from the outside world over a period of a couple hundred
>> years? To take an older form of Latin than is commonly
>> used in conlanging, and then remove it from all outside
>> influence, and see how it progresses seems to be a fun
>> idea.
> If the community were isolated from all outside influence
> (how & where?) I would expect development to be conservative
> rather like the way Icelandic has evolved from Old Norse.
> That in itself would give a different language from
> Classical Latin, since that language was subject to outside
> influences, especially from Greek - and certainly quite
> different from Vulgar Latin which was subject to all sorts
> of outside influences.
> --
> Ray
> ==================================
> ==================================
> If /ni/ can change into /¨»/, then practically
> anything can change into anything.