Have a look at the plate that Ron has already posted - if yours is Australia army your GVM is there (3652kg). GCM is not specifically specified in the manuals, so assuming GCM is GVM plus tow weight - again Ron's pic shows the tow weight (2 tons) so GCM is 5652kg - note the 2 ton tow capacity is in all conditions so on-road is probably much higher but not specified.  
The only workshop & user manuals are for british 101s (lower GVMs) so you will not find Australian documents for the information you ask. 
The original tyres are 9.00x 16 Tubed Goodyear Bar Treads - 10 Ply load rating not specified in the hand book.  Note there is no compliance plate nor tyre placards on 101s.
GS version - length overall, 4.330m, width 1.842m, height with canopy on 2.283m.  No idea about the ambulance version as they were not in use in Australia.  There are a couple of imports in country.
Determining when the vehicle was built can be difficult - certainly the 101s earmarked for Australia went to British Aerospace in the UK for conversion to Rapier Tractors in the second half of 1977 and were delivered to the army very late 77 into early 78.  However the vehicles themselves may have been actually built in 1976 - it is not clear - certainly from official sources.  My 101 on the NSW RTA documents has it build 01/77 which I believe is a default date.
You need to find out what you have - an ex Aust Army GS or an ex UK GS or even Ambo - the colour indicates an ex Aust 101, then you can workout where to go through the bureaucracy.  One thing is though if it has been previously registered in SA they should already have all the details you have asked for on file.  Before I registered mine in the ACT I gained information from the NSW RTA that confirmed what is was, is engine and Chassis numbers.  When I actually registered it in the ACT the authorities just pulled up full details on my vehicle even though it had never been previously registered in the ACT - in fact they even told me the Qld rego number that I thought it had previously was in fact not the correct number.
Hope this helps a little 
Good luck with it.
Garry
				
			 
			
		 
			
				
			
			
				REMLR 243
2007 Range Rover Sport TDV6
1977 FC 101 
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1973 Haflinger AP700
1971 Jaguar V12 E-Type Series 3 Roadster
1957 Series 1 88"
1957 Series 1 88" Station Wagon
			
			
		 
	
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