Regarding the Turfcat T436G, it looks like a Turfcat 400 Series (Model 66127 specifically) circa 1991-1993 with a 72" Deep Tunnel deck. The engine, Continental R11, is a Renault engine from France. The "R" in R11 stands for Renault. Renault was under license (at the time) with Teledyne Continental to provide this particular 4 cylinder, 36HP, gas engine.
To verify the engine, you might want to look at the alternator and see if there are French markings and or see if the engine nuts and bolts are metric as opposed to SAE, which Jacobsen rotary mowers were back then. The distributor probably says "Ducellier 2525565A". On the Continental name plate, it should also say "Made in France" to the right.
If you search in Google for "66127" and "Jacobsen" and you'll see all the hits specific to this model, including operating, maintenance, parts manuals or follow this link to the manuals:
There are a number of compatible parts for those Renault engines still around as well as Jacobsen parts on eBay, Craigslist, Amazon, OfferUp and a number of others. In the US, the French automobile Renault R11 (circa 1983-1991) was produced as the AMC Renault Alliance. So if you need some parts, there's still some cars around as well not just here, but all over the world.
Although you didn't mention any issues with the steering ram, if it leaks, instead of trying to rebuild or buy exact replacement, you might want to try a 1967 68 69 70 Ford Mustang and Mercury Comet power steering ram for $20 off eBay as they are compatible. The seals become brittle in these rams if they sit too long. Also, if the engine starts sputtering while under load, check your temperature gauge. If high (over 215), try blowing out the fins of the radiator with an air compressor to remove any built up crud. Also, the sister diesel mower is the Jacobsen T422D (Kubota diesel), of which a number of chassis, hydraulic, etc. parts are interchangeable.
Edited by jbx1066, May 12, 2018 - 08:36 AM.