The C35 is a real nice engine. Much less fussy than the G21. Top end isn't quite as fast, but they're not prone to crank breakage or trashing the rear bearing either and they're significantly lighter.

On 40% nitro turning a RevUp 8x8, a stock G21 would be guaranteed to puke the crank eventually and waste the rear bearing, but it would run a tad faster than a Fox 36XBB until it grenade'ed. That speed advantage started vanishing when the first Fox schnurle port combat special appeared circa 76' (the one based on a modified 36X case) and was completely gone by the time the Fox Mk3's and 4's appeared. The early schnurle Foxes had crank breakage issues too. I puked a couple during the runup to the 76 Nats. Duke had people attending the bigger contests handing out revised ones for free. Rick Brasher made some bullet proof cranks for the Mk2 (or maybe it was 3). I got two of those and never had another problem.

There is a standard Fafnir bearing that will replace the rear in the G21. The Fafnir's cage wasn't as prone to disintegration as the stock ST.