It does indeed look like a Mk.1 carrier.
So if you're using the 1/35 Tamiya kit (not that you have any choice in this scale!), you'll have to do the following.
- Leave off the towing hitch at the rear. Mk.1 carriers didn't have this.
- Leave off the 'steps' that hang down over the rear wheels and replace the front mud-guards with the earlier Mk 1. style (i'll get back to this).
- Remove all headlight detail and add the earlier larger headlights on each wing.
I agree with david on the 25pdr ammo boxes and that it is indeed a plank supporting them. As for other stowage it's hard to tell. They have obviously removed the spare road wheel from its place on the glacis and strapped it to the corner of the drivers compartment.
Also notice that the two 25pdr boxes in the first pic are absent in the second. There is something different (lower in height) under that tarpaulin which could be a german zeltbahn as David suggests, or just a dirty old tarp.
Now for the conversion!
David mentions the resicast ammo boxes and i'd suggest getting a resi-cast update kit (no. 35.128) if you want to do this properly.
Not only do some of the update kits include the earlier headlights and mud guards but they also vastly improve features of the kit like the oversize front compartment plate, the awful tracks (Tamiya ones are nothing like the real thing) and a hundred other details.
Eduard also does a great PE set to update the carrier although if you go the resicast route you won't need this (and it doesn't help with back-dating to a Mk.1) although I had to get mine from Canada (ebay) as I couldn't find it in the UK.
These can be seen at the following:
Resicast conversion reviews on PMMSresicast websiteResicast conversion at historex Eduard website (look for PE set 35364)
If you need any other info, or reference pics then please let me know as i'd be glad to help, this looks like it would be an interesting build.
Good luck,
James