engine swap?

hi all, i currently run an aq130 petrol on a 270 leg, does anyone know if an md 21b will fit on to the 270? or even if it is worth the hassle?any advice welcome

forgot to mention the md21b has a m3d gearbox(2:1) on it

It was once a version called AQ D21 - a dog!!
It even was a AQ D32 with the 6-cylinder version.

Hooked up to a 280 drive 1,61 - 1 ratio.
The AQ 130 has a 2.15:1, and the 270 may only use short hub propellers.
As a conclusion not something I would recommend.
Volvo Penta even sold a 'bastard' version with a MD21 -110S, MD 21 hooked onto a 110 sail drive which was a disaster as well.
The engine is not designed to run at the revs needed to get any boat planning, but if you are only into 'hull speed' as displacement boat, you may give it a try. I would however rather source a VW engine 1.8/2.0 for that task. Mercruiser have some in their range.

thanks for advice, ill leave it where it is, is there another oldish engine that anyone can recommend? the boat is a 20ft Wilson Flyer approx 1 1/2 - 2 ton cathedral hull with a 270 leg

It is all a question about how much money you want to put into it.
I would however not hook any diesel up to your 270 drive.
The 280 with 1.61 ration may handle the most, but then you need all connecting parts like flywheel housing etc.