200hp is not the limit of the rods at all. i am somewhere north of that now and the only thing stopping me from turning it up more is my transmission and the need for a bigger turbo. the issue is getting air into the engine. a holset hx35 should safely support 250-300 on a 617 with not horrible lag at least with a manual. i would of course fit the biggest intercooler you can and maybe consider water injection (not methanol since with the larger pump you wont need the extra fuel) for cooling if you will be towing. head work is good if you want the most out of it but i might not recommend it if your just aiming for a decently powerful tow rig.

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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
KD9AFT
A&P