Both ARP and Raceware (US companies) make stud kits for the D24T. By coincidence, as it happens I just priced them today for another motor build project. Raceware is $299 (USD) for a set of 14 studs, nuts, washers, and torquing instructions (D24T takes 14 head bolts or studs). ARP is $212 for a set for a VW 1.6 TD engine, which uses only 10 head bolts, so you need one-and-a-half kits, for $300+. Either one is excellent quality. I am going with the Raceware but others have used ARP with great results as well.
There is no upgraded bolt available, only the stock stretch bolt or the stud upgrade. You would only really need the studs if you were planning to run a major turbo boost increase over stock, though. At stock boost and fueling levels the stock headbolts are plenty adequate. There's no reason to spend the money to put studs in unless you have some major power adders installed elsewhere on the motor.
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86 745 D24T/ZF 345k lifted 2.5"
83 764 D24T/M46 155k
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