Travis I know you are thinking bike engine but just throwing it out there
how about 2 suzuki 3 cylinder sohc hemi 8v engines with a custom one piece
sump to hold the bottom secure, custom one piece inlet and exhaust manifolds
to hold the top secure and since you are up north and anything is almost
engineer-able a toyota 2ltr supercharger.
A bellhousing is available from sierras that can be modded for a w series
toyota gearbox and youl will have a 2liter hemi all alloy straight six.
74mm bore with 77mm stroke youll hit 1987cc.

straight 8 idea as reference

L8 buildup pages

How the blocks are honed or worked and pay the price of a 6 instead of 2 separate engiens
by bolting them up together for the machining.

It will be cheaper all up and the 3 cyl version is known to put out max hp over 200hp atw
and fitted to even porsches as a cheap replacement.

It will be totally balanced as a 6 unlike all 3 cyl designs.
You will have to offset one of the cranks at 120 degrees each? complete engine weighs 130lbs so times 2 minus extra alternator, starter, flywheel, clutch and other bits maybe 220lbs all up with lightened flywheel/ billet alloy clutch package thats round 105kg the same or lighter than an a15 complete with flywheel/clutch etc.

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