i would go for an os 21tm or just get another 3.3 but get a davis deisel rod and some ceramic bearing and build an ultra reliable 3.3
if you wanted to go nuts i would suggest a picco .26 or go a big block
LRP engines, nothing else. I am an LRP engine big fan. I tried also other engines but still I will go for LRP engines. Most especially for MT application.
I just got an O.S 21tm, they are a straight drop in replacement so no other mods needed, I did order a new 3 shoe clutch/flywheel because the standard revo set up isn't that crash hot. For the easiest engine swap with less parts needed then I think the 21tm is the best option.
Yes, but you may be hard pressed to find one that works with a pull-start. New era makes one but it hasn't been in stock for a long time. I have one of the new era mounts and a guy on this forum just received it as a loan to copy/make new mounts since they aren't around to buy.
I run an LRP28S3 in my revo with the new era bb leaner mount and a side pipe. At least that's what I run in the summer. I dropped a 3.3 in it while it's on loan and will probably leave it for winter running. Don't want to harm my LRP in cold weather, cold is hard on things.