rod/stroke ratio is no problem, perhaps not optimum, but should last 100,000 kms

Piston diameter is no problem -- A15 is the same as A14, and late model A12 blocks can usually handle that.

The size of the A15 crank throws is the problem. It is physically much bigger than A14. The little A14 cranks is radically machined to fit into A12 block, then rebalanced. I do not know if the A15 crank will fit.

should lat 100 thou k but will shake like a hula girl :)
1.48 without a very good balance and careful material clearancing
at the crank and inner block sides is asking for trouble.

Andy, 40 thou is 1 mm, & most A15's will overbore to 79 mm (3mm/120 thou), with some out to 80 mm (4 mm/160 thou). So if it'll clean up at 77 mm, the engine will be almost as strong as standard. All I can suggest for the seized pistons is a soak in some kerosene or some penetrating oil & some tapping out with a piece of wood & a hammer.

OK, here's the deal.

Firstly, there are only two cylinder block families if we disregard the three bearing A10 engine. [because it has only three mains so no other crank will swap into it]

Low deck blocks came with 70mm stroke cranks & 73mm bores for the A12, 75mm bores for the A12A & 76mm bores for the A13

Tall deck blocks came with 77mm stroke cranks & 73 mm bores for A13 [1974, US only] & 76mm bores for the A14. [yes, there were two different A13's]

They also came with an 82mm stroke crank with 76mm bore for the A15.

Now with a clever bit of combining of parts & a wee bit of simple machining one can install an A14 crank into any of the short deck blocks.
Machining? Hell, if you were loony enough you could even do it with a file.

It will be necessary to adopt a standard bore size of 76mm so that A15 pistons can be used & these will require the removal of a small amount of material from the crown at its thickest point.
In the case of the 1200 & A12 engines it will be necessary to either use A12A or short deck A13 rods, or alternately bore the rods out to accept the 19mm wrist pin of the A15 piston.
Standard A12A & A13 rods are just fine.

The problem is that at the bottom of the stroke the underside of the piston will collide with the counterweight of the A14 crank. The easiest way to fix this is to chuck the crank in a lathe & machine the overall diameter of the crank down until a sample rod & piston assembly can be fitted to the crank [while still in the lathe] & rotated around the crank completely without contact.
Some material is removed from the area alongside the crankpin during this process but not enough to be of some concern.

If you want, just file the counterweights down by hand, allow about a year for this task.

The A15 piston has its wrist pin located further up toward the crown meaning that the piston is shorter above the pin but the piston will still protrude a little from the top of the block, How much? I don't know but I believe it to be 0.5mm so slip those slugs in the bores & get out that handy dandy file again, or measure the protrusion & return to the lathe for some remedial machining.

Next, balance the whole assembly since we have just messed with all of the rotating/reciprocating weights & simply assemble it up just like a stocker.

The A15 crank? Forget it, there are practical limits to everything & an 82mm stroke in a short deck block is just a bridge too far.

Standard A series piston oversizes are 0.5mm, 1mm, & 1.5mm [20, 40 & 60 thou] so the A13 & A12A blocks can be safely bored to 77.5mm using standard or replacement A15 pistons. In a 1200 or A12 block this is probably pushing your luck but there is a local 1200 stroker engine around here with a 77mm bore & it goes like the clappers.

A15 crank in a short deck block. Forget it.
A14 crank in a short deck block. Eminently do-able.
Rod length to stroke ratio or rod angle? I don't know, that's your problem.

A14 crank machined for use in 1200 block.

1500 crank into a 1200 motor, it can and has been done, as far as know the motor I know of is still going.

Mr Muscle also works to clean up scuffed/seized bores, it eats the alloy and leaves the iron pretty much alone

I've heard from a few people that milk has something in it that frees up stuck motors a treat. I haven't tried it myself, (yet) But I have a stuck 265 hemi which will be getting this treatemnt as soon as the engine stand is free.

Quote:A15 crank into a 1200 or A12 cylinder block is a serious undertaking & I'd dearly love to see how this was done.
For me it fall into the area of diminishing returns in terms of cash outlay & work involved are concerned.

I suspect that some serious mods & or special parts were used as the A14 conversion is starting to push the practical limits as it is.
The chances of using a standard or modified piston seem small & the rod length is probably critical, so even a description would be keenly appreciated, but pictures would be wonderful.

A 38mm cranking with nutless motorbike conrod and pistons should provide enough sidewall clearance.
However the crank would need some serious work.