The common expert response to losing the ability to bid 2♥/limit raise/gf raise continuum, because we have been preempted past the cheapest raise, is to lower the miniumum for the 3♥ call... it becomes a good 2♥ raise, especially if based on 4 trumps. Lowering the minimum means that we lower the maximum as well: otherwise the range of 3♥ becomes too wide to permit opener any semblance of judgement. This means that good limit raises have to gf via 3♠... unless you want to use 4♥ as the good limit raise. However, that is problematic, expecially in hearts, because the auction is not necessarily over: we'd like our 4♥ bid to be well-defined lest 4th seat bid 4♠. So we would usually use 4♥ as a good playing hand, not very strong on hcp, and 3♠ as a good limit raise or better.
Using this style, which I think is quite popular in NA, we definitely lack 5 level safety when partner bids 4♥... and this is true regardless of whether we play 4♦ as Last Train.
As others have posted, there is no compelling reason not to place partner with wasted club values: indeed, his 4♥ call strongly suggests that... it virtually guarantees that if we play LTTC.
If we miss a good slam here, then I think that the odds are high that I will not approve of his 4♥ call.
I don't play 4♦ by partner as huge: it would have announced a non-sign-off hand, not a bust... and that is true in the partnerships in which we play LTTC and in those where we don't.
If you need significant extras, in your partnership, to bid 4♦, then either bid again here or change methods.. I suggest the latter, since you are reduced to guessing at this point in the auction.

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